For do-it-yourself stock traders, there's a lot of newsletter help to choose from

For investors who want to make trading decisions backed up by their own research, ''70% Off! The Investor's Guide to Discount Brokerage,'' by Mark D. Coler (with Ellis M. Ratner; Facts On File, New York, $24), lists six investment advisory publications that range from massive documents with thousands of pages of supporting information to small newsletters that simply give the author's buy-sell recommendations, perhaps accompanied by a telephone hot line where investors can hear the publisher's up-to-the-minute tips on the market.

These six were selected, the authors point out, because of their good investment records as measured by the Hulbert Financial Digest, another newsletter that grades the performance of investment advisory publications. While the letters are highly rated, following their recommendations requires special care. Even some of the advisers who write them acknowledge their predictions of stock performance are not infallible, or can be self-fulfilling, in the short term at least.

* Value Line Investment Survey. This is literally the biggest of the advisory services, with current information and detailed reports on 1,700 stocks. All these stocks are ranked according to how Value Line expects they will perform relative to the market. Stocks that are expected to do the best are given a 1; those thought to do most poorly get a 5. Investors should buy stocks ranked either 1 or 2, perhaps hold 3s, and sell 4s and 5s.

The $356-a-year price makes this the most expensive of the six (there is also a 10-week trial price of $37), but discounts can be found in Value Line ads in financial publications like Barron's. Or you can write Value Line, 711 Third Avenue, New York, N.Y. 10017, or call (212) 687-3965.

* The Zweig Forecast. Published by Martin Zweig, it includes a newsletter and a telephone service. Primarily through the daily-updated phone service, Mr. Zweig tells investors what to buy, when and at what price to buy or sell. It costs $245, or $50 for a three-month trial. Write The Zweig Forecast, 900 Third Avenue, 30th Floor, New York, N.Y., 10022, or call (212) 644-0040.

* The Professional Tape Reader. This is a newsletter-phone service edited by market technician Stan Weinstein. It includes mini-courses on specific investing topics and information on some 50 indicators Mr. Weinstein uses in his strict technical approach to investing. The cost is $30 for an introductory subscription of three issues, $150 for six months, $250 for a year, and $425 for two years. Write The Professional Tape Reader, PO Box 2407 Hollywood, Fla. 33022, or call 800-228-2028, ext. 497 (Nebraska residents, call 800-642-8300).

* Market Logic. This is published by Glen King Parker and Norman Fosback, his partner at the Institute for Econometric Research. It includes stock recommendations, discussions of mutual funds, and options, as well as summaries of what other newsletters are saying. Its price, including a phone service that is updated twice a week, is $195, but you can get a one-month trial subscription , or two issues, free. Write The Institute for Econometric Research, 3471 North Federal Highway, Fort Lauderdale, Fla. 33306, or call 800-327-6720 (Florida residents call (305) 563-9000, collect).

* Growth Stock Outlook. This letter, published by Charles Allmon, takes a fairly conservative approach to buying and selling, with an average annual turnover of about 25 percent. (Some newsletters have turnover rates of 100 to more than 200 percent a year.) Mr. Allmon follows about 100 growth companies with reasonable price/earnings ratios and advises selling them if their earnings drop below a certain level. Its cost is $125 a year, or $48 for a three-month trial. To subscribe, write Growth Stock Outlook, 4405 East West Highway, Bethesda, Md. 20814, or call (301) 654-5205.

* The Outlook. This weekly newsletter, published by Standard & Poor's, looks at specific stocks and industries, provides a market overview, and updates its portfolio of 50 stocks. It is more conservative than some of the others, but it does have more than 45,000 subscribers. It is $175 a year, $30 for a 13-week trial subscription. Write The Outlook, Standard & Poor's, 25 Broadway, New York, N.Y. 10004, or call 800-852-5200.

Finally, the author of ''70% Off!'' has a newsletter of his own on the discount-brokerage business, which includes information on commission rates brokers are charging for various services, changes in the industry, and updates on the stock market. Its cost is $195 a year, or $37.50 for four months, but you can get a free copy by sending a stamped, self-addressed business envelope to Discount Brokerage Advisory Service, 200 Park Avenue, Suite 303 East, New York, N.Y. 10166.