California also retained its status as home to more of America's wealthiest than any other state, with 80 of the top 400, up from 77 in the 1993 survey. New York remained in second place with 53, down from 57 a year ago.
In its annual report on the cream of the capitalist crop, the biweekly business journal put Gates' net worth at $9.35 billion, enough to bump Buffett, with $9.2 billion, out of the No. 1 post he held last year.
Forbes attributed the flip-flop to the vagaries of the stock market.
Buffett, 64, the folksy investor from Omaha, Neb., kept his investment company, Berkshire Hathaway, growing this year, but not as fast as Microsoft.
Thanks to his holdings in the company, Gates' net worth grew by more than $3 billion while Buffett's rose by a comparatively paltry $900 million.
The year has been one of milestones for Gates, 38, of Bellevue, Wash., and his company.
On New Year's Day, the king of the computer nerds married Melinda French in Hawaii. More important for Gates' wealth, Microsoft emerged largely unscathed from a federal antitrust inquiry into its alleged monopolization of the software business.
Gates is quoted in the Oct. 17 Forbes as saying its list is "silly." He appears to shun such marks of success. "If I'd had some set idea of a finish line, don't you think I would have crossed it years ago?" he said.
Forbes also said Gates now appears to be the wealthiest commoner in the world.
The only foreign billionaire in his league besides royalty is Yoshiaki Tsutsumi, a Japanese railroad and hotel tycoon whom Forbes said is worth $8.5 billion.
Coming in third for the second year in a row was John Kluge, 80, of Charlottesville, Va., who built the Metromedia radio and television station empire, then liquidated it to invest in movies, restaurants and long-distance telephone service.
Kluge's restaurant and movie interests are recovering from some weak times, Forbes reported, and the long-distance company, LDDS, is now No. 4 behind AT&T;, MCI and Sprint. Kluge, whose worth was listed at $5.9 billion, led the list from 1989-91.
The stock market's bouts of weakness this year didn't hurt Edward Johnson III, 64, of Boston, chief of Fidelity Investments, the top mutual fund company. His $5.1 billion was enough to vault him to No. 4, from No. 38 last year.
Amway Corp. partner Richard DeVos, 68, of Ada, Mich., rounded out the top five with $4.5 billion, up from No. 33.
Money losers whose fortunes dropped off the list include onetime Hollywood kingpin Barry Diller. His declining shares in home shopping channel QVC Inc. dropped him to $130 million, from last year's $345 million.
As in past years, the list shows moguls who make their millions from the dirty smokestacks of oil, gas and manufacturing are losing ground to those in clean-burning companies like technology, retailing, finance and entertainment.
Here are the Top 15 on the Forbes list of the 400 richest Americans.
'94 '93 rank Hometown rank Name 1 2 William Gates Bellevue, Wash. 2 1 Warren Buffett Omaha, Neb. 3 3 John Kluge Charlottesville, Va. 4 38 Edward Crosby Johnson III Boston 5 33 Richard Marvin DeVos Ada, Mich. 6 12 Ronald Owen Perelman New York 7 34 Jay Van Andel Ada, Mich. 8 9 Alice L. Walton Rogers, Ark. 9 5 Helen Walton Bentonville, Ark. 10 8 Jim C. Walton Bentonville, Ark. 11 7 John T. Walton San Diego 12 6 S. Robson Walton Bentonville, Ark. 13 10 Keith Rupert Murdoch New York 14 14 Donald Edward Newhouse New York 15 13 Samuel I. Newhouse Jr. New York
'94 Net worth rank (billions) 1 $9.35 2 9.20 3 5.90 4 5.10 5 4.50 6 4.50 7 4.50 8 4.34 9 4.34 10 4.34 11 4.34 12 4.34 13 4.00 14 4.00 15 4.00