Ah, ambiance!

Some fine day you may find yourself in Winterport, Maine, and desire a restaurant with ambiance. Have you noticed how the somewhat inappropriate word ambiance has been picked up by the victualers for that ''undefinable something'' which is perhaps meant to make a hot dog taste like pheasant under glass and convert a vernacularized greasy spoon into a salon of delicate gusto?

Take a place without ambiance, and what have you got? Ambiance, derived from ambient, is supposed to mean a mood, quality, tone, atmosphere - possibly an advertising effort to come up with an English Gemutlichkeit. Ambiance is not in the little dictionaries - only in the fat one. Most of the places touted to me as loaded with ambiance turn out to be just other places, and we have concluded ambiance is poor fare when you need to eat. In Winterport, on that fine day, try the Drydock.

Winterport's main street runs along the Penobscot River; the town was so named because it was the limit of navigation during the freeze-up of a Maine winter. In 1766 it consisted of two log houses. Today it is more settled. It sits on US Route 1-A, which goes to Bangor, and the Drydock is not a prominent part of that Main Street. It has no neons to proclaim its ambiance. The summertime screen door allows the wintertime door to stand open, so from the sidewalk one doesn't see the sign that says it is open, and a customer will want to peep in to see if business is ambient - the evidence coming from the gentlemen at the five-stool counter taking their desserts of three-inch chocolate cream pie with two-inch topping.

When you step in, as we did, the gentlemen will turn to nod, offering that Winterport is friendly and the natives disposed to trade. Nancy Morrill, the waitress, will bid you welcome and state the daily special, which is also posted on a chalk-board. Or you can select your choice from round targets over the counter, inked with a felt pen: fried or baked haddock; fried chicken; fried clams; fried shrimp; ham steaks; fried scallops; hamburg steaks; and the coup du jour of baked haddock, egg sauce, mashed potatoes, green peas, and roll, $3.95. The only dissonance in the pervading ambiance is the smacking of lips by the gentlemen at the counter.

We had to go that way on a thick-o'-tourist day, to pick up Grandson Tom, who had been attending a basketball clinic at the University of Maine at Orono, pronounced or'no. We sped past many roadside enticements, restaurant after restaurant with prominent ambiance, and with good sense and good fortune came to the Drydock.

It was clearly not tourist oriented, and feeds only people. Besides the five stools, the Drydock has six tables. Nancy told us we could sit anywhere we wanted to, it was all right with her, and this was a bit of a tip-off, since ambiance usually has a sign saying ''Please Wait To Be Seated.''

The place was spotlessly clean, and Nancy kept wiping and polishing as she served. Kelly Higgins, female, was cooking, and we surmised her youth precluded the experience of a Cordon Bleu certificate. We were right. She seemed dubious about the Cordon Bleu, and I thought was even hesitant about ''certificate.'' She readily told us when we asked that she is 20. I'd have guessed 16. Superb!

And while we dined the tourists rolled by in battalions, some going and some coming, but we were pleasantly detached from vacationism. Then we noticed the pictures on the walls. For some time the Drydock has been asking its guests to bring in snapshots to be tacked up. Hundreds and hundreds of happy faces smiling approval of Drydock ambiance - Nancy said each is identified and dated on reverse. I gave her my wallet picture of Grandsons Bill and Tom, who are now near the baked haddock and the homemade fried onion rings.

Then, in an ambient inclusiveness that made us feel like partners in the business, Nancy brought all the money from the cash register to the corner table and counted it. The gentlemen had left the counter, and the noon business was about over. Kelly was leaving for the afternoon. Nancy stacked the coins, and smoothed and faced the bills. ''Did we make enough,'' I asked, ''so you can take me to the dance tonight?''

''Ayeh,'' she said. ''Sure did!'' Ambiently.