New York ? It looks like the U.S. billionaire’s club isn’t quite as exclusive as it once was.

There are now 313 billionaires in the United States, the largest number ever and a huge jump past the 262 counted last year, according to Forbes magazine, which Thursday released its annual ranking of the 400 richest Americans.

The combined net worth of the 400 rose $45 billion and reached $1 trillion this year for the first time since 2000, before the dot-com bust wiped out billions of dollars in wealth.

The biggest billionaire of all was again Microsoft Corp. founder Bill Gates, whose $48 billion in estimated wealth was up $2 billion from 2003. Gates again was followed by investor Warren Buffett with $41 billion, the list’s biggest dollar gainer with a $5 billion increase, and Microsoft co-founder Paul Allen, who held the No. 3 spot although his net worth fell $2 billion to $20 billion.

Members of the Walton family, whose fortune comes from Wal-Mart Stores Inc., again swept spots four through eight, with each having estimated wealth of $18 billion.

The only tweak in the top 10 from last year came from Dell Computer Inc.’s Michael Dell and Oracle Corp.’s Lawrence Ellison, now No. 9 and No. 10 respectively after swapping places from 2003. Dell Computer stock has weathered the tech slump relatively well during the past year, giving Michael Dell a net worth of $14.2 billion. Ellison, whose stock has suffered, had $13.7 billion in holdings, a drop from $18 billion last year.

There are 45 new names on the list, including Google’s Sergey Brin and Larry E. Page — also the youngest members of the 400 at 31. The two tied for No. 43 with $4 billion each after their company’s stock went public in August.

Microsoft founder Bill Gates , shown in this January file photo, talks about software and hardware innovations in his keynote address at the 2004 Consumer Electronics Show in Las Vegas. Gates is the wealthiest person in America, according to Forbes magazine, with a net worth of 8 billion.

Forbes senior editor Peter Newcomb attributed the overall gains in the list to the improving economy, as well as a good year in the financial sector and industries including food and wine.

Casino mogul Steve Wynn, who climbed to No. 215 from No. 377 last year, saw the largest percentage increase in wealth — a 100 percent jump to $1.3 billion from $650 million. Last year’s biggest dollar gainer, Amazon’s Jeff Bezos, received the less-coveted title of biggest dollar loser this year with an $800 million drop.

Fifty-four people dropped off the list from last year, including such notables as Disney’s Michael Eisner, BET’s Robert Johnson and Monster.com’s Andrew McKelvey.