NEW YORK, DEC. 16 -- Henry Kaufman and Allen Sinai, two of Wall Street's best-known economists and market gurus, are giving up their current posts at major investment firms.

Salomon Brothers Inc. announced today that Kaufman, whose gloomy forecasts in the early 1980s earned him the nickname "Dr. Doom," would leave early next year to form his own consulting firm.

Kaufman is currently a managing director, senior economist and head of research at Salomon Brothers.

Sources said, meanwhile, that Sinai was dropping the job of chief economist at Shearson Lehman Bros. Inc. but planned to remain with the firm in a more "entreprenurial" capacity outside the company's New York headquarters.

Kaufman, 60, is believed to be the best paid economist in New York's financial district. In 1984 his salary and bonuses were estimated to total about $2 million.

His economic prognostications were often forceful market movers several years ago, but they have had a lesser impact recently.

Salomon spokesman Robert S. Salomon Jr. said Kaufman's impact today is "certainly less than it was in 1982.

"From time to time markets and investors have hung on his every word," Salomon said. "The peak, in terms of his impact, was most probably in 1982."

Friction between Kaufman and Salomon Brothers management is believed to have existed for several years. Kaufman reportedly objected to the firm's increased role in the junk bond market.

Kaufman resigned as a vice chairman in October 1986 in a move Salomon executives said was intended to allow younger managers to play a more prominent role in the firm.

Salomon is cutting costs as part of a broad-based restructuring.

Kaufman joined Salomon 26 years ago as an analyst in the company's fledgling research department.

Sinai, 48, gained increasing prominence during the October stock market crash. He has been widely quoted and has made numerous television appearances during which he interpreted events.

A source close to Shearson said Sinai, who lives in Lexington, Mass., outside Boston but works in New York during the week, had been discussing a move for "a minimum of 10 months."

According to the source, Sinai wants a position "a little more entrepreneurial in nature" and the opportunity to work closer to home.