The United States Football League gained much-needed credibility and financial support yesterday by signing a two-year, 40-game agreement with the ABC television network.

Although the value of the contract was not announced, it is believed to be worth approximately $20 million to the league, which would give each of the 12 teams about $830,000 per year.

"I don't believe any new league has ever gotten a (network) television contract before playing its first game," said Peter Spivak, USFL acting chairman. "I never had any doubt about our credibility, but this should convince others that we are very serious about this venture. It shows everyone that the 'other' season is a reality."

"I guess we're not surprised," said Jim Heffernan, the NFL's director of public relations. "There is no exclusivity clause in our contract with ABC or anyone else. As far as competition for players, it is up to them how much they want to compete."

The USFL, which includes a Washington franchise, will play its games from March to July, starting next spring. ABC, which has an option for two more years, agreed to telecast 20 games per year, including a Sunday game of the week, one prime time night game each week and all the playoff games, ending with a July 4 championship game. There will be no local blackouts of games that are not sold out.

The new league is continuing negotiations with cable networks to televise additional games next season.

"With the exception of some events like the Kentucky Derby and the Indianapolis 500, there have not been sporting events during the March to June time of the year that have captured the public, and it's generally a down period for us," said Roone Arledge, president of ABC news and sports, at a New York press conference yesterday. "We think this sport has the potential to do that and it has the advantage of not going directly against college football or the National Football League."