LIBERTY - Although the nation's roll of billionaires is growing fast, Sullivan County's Alan Gerry has secured a spot on Forbes Magazine's list of America's 400 richest people for the fifth consecutive year.

In the magazine's Oct. 13 issue, now on newsstands, the cable television magnate ranked No. 181 with a fortune of $970 million. Gerry's recent plans to develop the original Woodstock festival site in the Town of Bethel earned him a photograph in Forbes, sitting atop the stone memorializing Max Yasgur's famous field and dubbed, ''Counter-Culture Curator.''

Forbes started compiling the list of richest Americans in 1982, when there were only 13 billionaires. Now there are 170, and a minimum net worth of $475 million is necessary to make the magazine's cut.

Bill Gates, the 41-year-old head of Bellevue, Wash.-based Microsoft, has a comfortable lead at the top of the list with $40 billion after doubling his net worth in the past year. He is considered the world's richest person, including royalty. (The Sultan of Brunei is believed to be worth a mere $38 billion.)

Gates' galloping net worth has increased the gap between him and runner-up Warren Buffett. Buffet, the investor from Omaha, Neb., is worth $21 billion, according to Forbes. He is the only billionaire in the top five who did not make his fortune in a computer-related field.

Oakleigh Blakeman Thorne III, of Millbrook in Dutchess County, was listed with $720 million at No. 254. Thorne helped run a family business, CCH, which became the largest publisher of tax guides for lawyers, accountants and government - with the Internal Revenue Service being the biggest subscriber. The Thornes sold the company last year and doubled the family fortune.

Gerry, 68, of Naples, Fla., and Liberty, started out as a television repairman and antenna installer. He built his Cablevision Industries from a small, five-channel system founded in Liberty in 1957 into a national cable empire.

CVI had more than a million subscribers across the country when Gerry sold the company to Time Warner for $2.6 billion in 1995 - when he was already on the Forbes list. Gerry entered the list in 1993 with a rank of 266 and a net worth of $400 million.

Gerry then formed Granite Associates with a handful of key CVI executives. The group bought the site of the 1969 Woodstock festival last year for $1 million, and reportedly spent another $1 million to $2 million acquiring 1,000 acres around it.

The area, as big as Central Park in New York City, is slated to be the home of a performing arts and entertainment center and has been hailed as having the potential to revive Sullivan County's economy. The Catskills' famous resorts have fallen on hard times and the state Legislature has rebuffed lobbying to bring casino gambling to the region.

Gerry did not return calls for comment yesterday, but other Sullivan County folks did to salute his generosity and community consciousness.

''It has been wonderful to know Alan Gerry and see his support,'' said Jonathan Drapkin, Sullivan County manager. ''He is one of the most intriguing people I've had the opportunity to meet and I'm completely surprised to find him as approachable as he is.''

Michael Sullivan, president of the Sullivan County Partnership, called Gerry, ''... the ultimate self-made man, a standup guy, an ex-Marine who has lived that code and been terrific for Sullivan County.''

In the mid-1980s, New York had 80 people on the Forbes list, tops in the nation. But wealth continues to head west: California claims the lead once again with 83 members, compared to 47 from New York.

Forbes said it estimates wealth with the help of experts and authorities who follow particular industries. In instances where fortunes are tied to publicly-traded stock, the magazine based worth on share prices at the market's close on Aug. 22. Private companies are more difficult to value, with observers looking at multiples of cash flow, earnings or sales. All in all, ''highly educated guesses'' are used, the magazine said.