Psst! Want a hot stock tip? How about General Public Utilities and Babcock & Wilcox, most recently in the news as the owner and builder, respectively, of the Three Mile Island nuclear plant?

Most investors would prefer to stay as far away from these stocks at the moment as from the radioactive facility near Harrisburg. Not Bob Torray. He recently bought General Public Utilities and McDermott, the parent company of Babcock & Wilcox, as well as Westinghouse, another nuclear plant builder.

Lest you conclude he has been exposed to a high dose of dementia, consider that Robert E. Torray, 42, heads of the country's most successful investment firm. During the first quarter of 1979, Torray Clark & Company of Chevy Chase outperformed all other independent investment advisors managing assets of $100 million or more in stocks, according to the first such records filed with the Securities and Exchange Commission and analyzed by Computor Directions Advisors Inc. of Silver Spring.

Torray Clark increased its return on the equity portion of its portfolio by 16.8 percent at the same time the Standard & Poor 500 stock index rose 7.1 percent. The median return for all investment advisors reporting to the SEC was 6.2 percent.

"I'm not overly thrilled (at being number one) because it represents such a short period of time," Torray said yesterday in an interview, adding, "No one in the industry has done as well as we have for years."

Indeed, according to Frank Russell Co., a private firm ranking investment companies, Torray Clark has been number one most of the time. Its eight-year average gain in assets, even during the worst recession since the 1930s, was 13 percent, compared with 4.6 perceny by the S&P. In the past five years, Torray Clark has averaged 20 percent. Of the 176 companies in which it has invested in eight years it has lost money on the stock of only 12, a 93 percent success record.

Torray (pronounced Tor-RAY after he changed it from the French Thore) and his partner, David Clark, were both employed by Blyth Eastman Dillon until they struck out on their own in 1972. They took with them five pension fund clients. Their eight-person firm now handles investments of more than $300 million for 24 corporate and labor pension funds and university endowment funds. The minimum portfolio size required is $10 million.

While Wall Street is scrambling to fill portfolios with stocks that can weather an expected recession later this year, Bob Torray does not appear overly concerned. "A recession may last a year or two," he said, "but we are interested in holding our stocks for two or three years or longer."

As such Torray Clark bought heavily in the last quarter of 1978, filling its portfolio with large industrials such as mining, chemical and paper/forest company stocks. The other third of its portfolio consists of bonds and Treasury bills. For now Torray Clark is more or less biding its time.

Torray Clark currently has a portfolio of 86 common stocks, listed for public inspection at the SEC. Torray was asked if the average investor, beaten down by poor showings in the market for years, could realize comparable gains by imitating his investments on a smaller scale.

Torray laughed and shook his head. "It would be extremely difficult to implement for individuals," he answered. "First they don't have enough money. Secondly, they don't have enough patience. And finally, (his firm's) type of investing goes against human nature. People always want to buy when the market is up and sell when it goes down.

Buy low, sell high. "Our investment process is so simple," Torray told a magazine for professional investors, "that some people do not see how it can work." Yet work it does. Torray Clark may even succeed in turning the Three Mile Island disaster into a victory for its clients. CAPTION: Picture, Robert Torray, head of Torray Clark & Co., during interview at his office. By James A. Parcell - The Washington Post