Choosing the right gear for a trek: your first important decision

Selecting clothing and equipment for a trek or outdoor adventure is like trying to find your way through a labyrinth. Simplicity is what you are after; less is definitely more. But more is what continues to appear each year in what has become a major industry. There are options and compromises involved in every purchase.

Even to the seasoned trekker, annual developments in synthetic fibers and new principles of insulation can be bewildering. There is no such thing as ''just buying the best.'' There can be a whole array of ''best,'' depending on how high you go, how rugged the terrain, how wet the climate, and how much you yourself will be expected to carry.

The most important decision you can make is to begin early and to plan well.

First, know as exactly as possible what conditions you are preparing for. Will you be backpacking and carrying all your gear (in which case the primary consideration will be ounces)? Or will you be carrying a daypack - with yaks, porters, kayaks, or Land-Rovers carrying the support equipment? What will the weather be like? High altitudes, for example, mean potentially great extremes in temperatures, from warmer-than-normal sun to sudden freezing storms. A wet, cold climate requires parka, sleeping bag, and underwear that will withstand soakings without losing insulating properties.

Think about what you will be doing. Climbing out of rafts for on-shore expeditions from a cruise ship demands knee-high Wellingtons just as much as does kayak-touring. And keeping your feet dry is often not just a matter of comfort - if, for example, you happen to be in a glacial fjord in Alaska.

All this is further complicated by whether you are willing to buy equipment solely for one trip, or wish it to be versatile enough to serve you for many trips.

Second, read the list of recommendations that will be sent by the travel organization. If it is good enough for you to have chosen to travel with it, it should know the country. But temper the advice with your own experienced preferences and well-educated choices.

Third, buy good-quality equipment made by reliable companies and sold at good outfitting stores. At 17,500 feet in Nepal, an extra $20 will seem insignificant , but the state of your cold fingers will not. You can also do research as you shop; most salespeople are avid outdoors specialists.

The basics. The most fundamental principle of dressing for the outdoors is what is called ''layering.'' Layering for a trek in the Andes could consist of a long-sleeved, cotton-synthetic blend shirt, a medium-weight wool sweater, and a rainproof windbreaker or Thinsulate parka. Another combination for lower altitude could add a tank top undershirt, eliminating the parka.

Some people would juggle the parts to substitute a lightweight turtleneck or a polypropylene jacket. In extreme cold but with heavy exertion, you would add lightweight thermal underwear. For sedentary activity in extreme cold, the combination would include heavyweight thermal underwear and a down parka. The fine-tuning is a matter of individual preference - always with an eye to conditions of weather and exertion.

Layering allows you to go from a cold morning to midday sun, to adjust after a long climb while sitting at 13,000 feet. It also keeps you warmer, because the layers trap air.

Function in dress is primary. To facilitate layering and to allow comfortable freedom of movement, all clothes should be roomy. Fashion fit has no place in trekking. Women can try men's small sizes or boys' sizes in shirts to obtain a fuller cut and a longer arm and tail length. Pants and shirts should be full length (to protect against briers, sun, and, alas, insects), but if they are loose they can be rolled up. All clothes are more useful if they have pockets with buttons, Velcro, or snaps.

Wool and synthetic blends are the materials of choice for trousers and shirts. There are natural-fiber enthusiasts who insist on the feel of cotton, but synthetics dry faster and are less heavy when wet. Wool (pants and sweater) is mandatory for cold weather. It keeps you warmer when it is wet, and if it has the natural oils left in, it will tend to shed water. Its only drawback is that it is heavy. A recent improvement in walking pants is a spandex blend that allows stretch.

Polypropylene is the clear choice for thermal underwear. It keeps moisture away from the body in addition to insulating, thus preventing chill after heavy exertion. It also dries fast and is light.

For cold weather, mittens are warmer than gloves, and again wool is my recommendation, Dachstein mittens specifically. They are preshrunk and thus very dense, and the natural oils are left in. They wear like iron, are flexible, and keep even cold-natured hands warm after a total dunking in glacial meltwater. For ease of camera operation, there are warm-fabric glove alternatives: polypropylene, silk, wool of course, and space-technology silver.

Wear two pairs of socks with boots: wool outer and an inner liner of polypropylene, silk, or thin wool.

Some essentials you should always consider are a hat with a visor and brim (some are made now with under-brim green that is restful to eyes), dark glasses (very important near snow and ice), extra glasses if you wear a prescription, a wool hat or balaclava, a Swiss Army knife, a space blanket, a lightweight small flashlight with extra batteries and bulb, fly dope (serious outdoors strength is what you'll want when you are out there in the tundra or on the Amazon), a leakproof plastic water bottle, some means of water purification, sun screen (some total block-out even if you cherish a dark tan - the sun at high altitude burns), Sno-seal (carried with you for boots even though you have treated your boots just before leaving, since it wears off), and gaiters.

A cardinal rule is to take the minimum. Having just one of most items is the limit. Only in thermal underwear, trousers, and shirt may you take a spare in case of drenching. Two sets of socks are sufficient, but a third is frequently recommended for the same drenching reasons.

The last basic principle, but one that will ease your life immeasurably on the trail, is compartmentalization. A place for everything, and everything in its place. You will not relish rummaging through a loosely packed duffel after the first day. Plastic Ziploc bags are perfect, although you can buy expensive different-colored stuff sacks.

The choices. In three areas, all critical to your comfort, substantially different choices in equipment are available. Substantially different, strongly held opinions are also available. The complexities are great, and I advise extensive research.

* Synthetic insulation vs. down: Nothing is so warm and so efficient in terms of weight and compactness as down. But when down gets wet, it loses the loft that keeps you warm. Synthetic insulation not only dries out fast, but it keeps you warm even while it is wet. In cold-climate, wet situations such as the Andes or southeastern Alaska, synthetics are something to consider. Some of the new materials are Thinsulate (you may mistrust it because it is in fact thin, but it will keep you very warm), Quallofill (a new material not yet in extensive use but considered by many to be the future synthetic), Polaguard, and Polaloft.

* Goretex vs. foul-weather gear: Goretex is not waterproof. It will not withstand a downpour. In addition, water gets in through every single sewn seam. If the seams are labeled ''factory sealed,'' it means the ''major seams'' are; and it is an intricate and virtually impossible job to seal the remaining seams yourself with the special sealant manufactured by Goretex.

Goretex is also subject to having the laminate that creates the waterproof quality worn away by heavy use (such as trekking) and by dirt (unavoidable in three weeks on the trail). The new ''superlight'' Goretex is even less durable. Goretex is, however, a good material for an expensive wind-suit.

Foul-weather gear will keep you dry. But it will also trap perspiration. It is heavier than Goretex, but there are new lightweight and rugged makes available.

* Leather boots vs. Goretex: Goretex boots can be half the weight of leather boots, thus giving you a sense of freedom on the trail. They are not so water-resistant as well-made, Sno-sealed leather boots, and they do not provide the same support. If you are considering Goretex boots, be certain that they have no sewn-through seams and that they are very well constructed; famous brand names can be misleading. In leather boots, look for construction that will keep the boot watertight to the top (for example, a tongue that is joined to the sides of the shoe). Avoid the more supple leathers; they require less breaking in, but provide less support.

Trip-enhancing extras. I suggest a compass, a magnifying glass (miniature fold-up models of excellent quality are available), good, high-powered, lightweight binoculars (the better the optical quality, the better you will see the puffins in the Pribilofs), and a camera that is water- and dust-resistant. I find a photographer's vest a boon in cities, but so unbalancing for serious hiking and kayaking that it interferes with the experience. Important supporting materials are packages of desiccant for film, plastic Ziploc bags for film and spare lenses, and plenty of lens tissue and cleaning fluid (available water may be gritty).

Lead shield bags for airport security are heavy, and some airports and airlines use X-ray machines that penetrate the bags. Subjecting film to the X-rays does alter it, especially if you have to go through several security checks. Hand-carry film and smile nicely.

Logistics and special suggestions. Take your boots on the plane along with your camera and film. I have never in many years of extensive travel had a bag lost, but you yourself know that is not the norm. Film is hard to find, expensive, and probably out of date where you will be going. Good boots in your size are almost certainly not to be found. City clothes can be minimized (or eliminated) and baggage simplified by a judicious choice of colors and cuts in trail clothes.

A walking stick is wonderful for balancing during stream crossings and for walking downhill on steep, rough terrain.

Label every piece of equipment clearly with a waterproof pen. Other trip members will doubtless have identical makes. Padlocks on every duffel (and on your daypack in town and city) make theft slightly more difficult and obvious.