A couple of stock-pickers with a fervent following

What are the two ''hottest'' numbers on Wall Street? Ask any stockbroker and they tell you: the ''hot lines,'' or phone numbers of the taped messages of market seers Stan Weinstein and Marty Zweig. On the day after a new taping, the market is apt to react immediately.

Two weeks ago Mr. Weinstein, who writes a newsletter called The Professional Tape Reader, recommended buying the semiconductor stocks. The next day, Texas Instruments, National Semiconductor, and Advanced Micro Devices spurted. The same is true with Mr. Zweig, who publishes the Zweig Forecast newsletter. Recently he recommended that his clients buy Metro Tel (over the counter), and the stock opened 20 to 30 percent higher than it had closed the previous day. On almost any of his American Stock Exchange or OTC recommendations, the stocks open up sharply higher.

The phone numbers are so hot, in fact, that both Weinstein and Zweig change the numbers every 10 to 12 weeks to keep nonsubscriber calls to a minimum. But both market predictors admit they receive a lot more phone calls than they have subscribers. For example, Zweig has some 12,500 subscribers. When the market dropped 38 points last fall, he received 19,000 phone calls in one night. ''People were scared,'' he recalls, ''so they called like crazy.''

To get the unlisted numbers, investors call other investors who subscribe to the services. Brokers give the numbers to their customers as ''gifts,'' which makes Zweig mad.

The reason Zweig and Weinstein have become so popular is that they have accurately picked both the direction and the best-performing stocks in the current bull market. According to the Washington, D.C.-based-Hulbert Financial Digest, which rates the advisory letters, Weinstein was up 56.4 percent in 1982, while Zweig was up 80.3 percent. Theirs were the No. 1 and No. 3 newsletters in the business. No. 2, the Boswell Report, up 57.6 percent, does not have a phone service.

With so many investors calling in to get stock recommendations, some market observers complain the market seers are successful because they have become self-fulfilling prophets. Mr. Weinstein, in a phone interview, doesn't dispute that his recommendations can move a stock, or industry group, for a few days. But he comments, ''There may be a lot of buying for a day or two, but when it gets beyond that, the market plays out its script. . . . Over a period of time, the market is bigger than Stan Weinstein.''

Mr. Zweig says he feels his recommendations are sometimes ''self-defeating.''

The stock market predictor says it ''drives me crazy'' when his stock recommendations open on ''big gaps,'' that is, sharply higher than the previous day's close. ''My guys are getting hurt,'' he complains, explaining that when he recommends a stock at $20 a share and it opens at $24 a share, his subscribers have to buy the stock at the higher price.

In fact, Zweig thinks sometimes the marketmakers or specialists are out to fleece his subscribers. ''They (the specialists) think they (my subscribers) are just a bunch of sheep, and if they can (boost) the stock price they can make a quick profit.''

Recently, to cut down on such moves, he has recommended that his subscribers place stock orders using ''limit orders.'' Thus, an investor places an order to buy the stock at a price no higher than say $21.50. On one recent day, he says, he recommended seven stocks using ''limit orders'' and was able to buy three of them. The four others opened higher than his limit. ''If the investors don't listen to me,'' he asks, ''what can I do?'' When the market soared in the fall, he admits, ''it got progressively worse,'' as investors' greed overtook their common sense. ''They got frenzied,'' he says, noting that right after the election it was so bad he was upset when he went home.

So what are Weinstein and Zweig saying about the market now? And what stocks do they like?

Weinstein says he continues to believe the long-term trend is ''super bullish.'' Over the intermediate term (anything beyond the next few trading sessions), he is likewise bullish. Over the short term, however - the next few trading sessions - he said last week that the markets could be ''sloppy.'' He added, ''We have definitely reached a more selective point in the rally, where the early leaders are starting to lag.'' Now, he says, the companies that lagged are coming to the fore. He specifically likes the energy stocks, some of the basic-industry stocks, selected technology companies, and the semiconductor stocks.

Zweig is likewise bullish over the long term. But over the intermediate term he's only ''moderately bullish.'' As to his stock selections, he says he looks for companies with strongly rising earnings and ''a nice stock price action as well, as long as the price-to-earnings multiple is not out of sight.'' Recently he started buying some of the basic-industry stocks and some energy companies, including Pittston, a coal producer, Standard Oil of Ohio, and Phillips Petroleum. He still likes the gold stocks, which he says were among his best performers. His recommendations of smaller companies, however, have the biggest following, since they react much faster. ''When I recommend a basic-industry stock, like US Steel,'' says Zweig, ''the subcribers just yawn. But when I recommend a high-technology company, they say, 'He must know something.' ''

Weinstein's newsletter costs $250 a year, $150 for six months, and $30 for a trial subscription. (It can be bought by calling a toll-free number, 800-228- 2028, ext. 497. Zweig's letter costs $245 a year and can be obtained by writing to the Zweig Forecast, 31st floor, 747 Third Avenue, New York, N.Y. 10017.