The U.S. Football League has extended its deadline for the owners of the Washington Federals to either sell the team or have it taken over by the league, a source close to the negotiations said yesterday.

The league had given the Federals until midnight Friday, but the deadline was extended in exchange for the Federals waiving their claim of territorial rights if an existing USFL team moves to Baltimore, the source said.

According to this source, at least three current USFL teams are interested in moving to Baltimore when the two-year-old league begins head-to-head play against the National Football League in the fall of 1986.

Myles Tanenbaum, owner of the USFL-champion Philadelphia Stars, announced last month that he wanted to move to Baltimore for the 1986 season because he could not compete against the NFL Eagles or baseball's Phillies in Veterans Stadium in the fall.

The source identified the Pittsburgh Maulers and Michigan Panthers as other teams exploring the possibility of moving to Baltimore, which does not have a pro football team because the Colts moved to Indianapolis.

League and team sources were unavailable for comment last night.

Meanwhile, newspapers in Florida were reporting that Donald Dizney, an Orlando hospital executive, signed a 34-page contract late yesterday afternoon to purchase the Federals.

The sale price, according to sources, is $3 million and 20 percent of the new, limited partnership that will own the team. However, according to a source close to the deal, Dizney will pay only $1 million cash when the sale is closed.

The remaining $2 million will be paid from Orlando's share of future league television revenues and that payment is contingent upon the continuation of the league, the source said. The current franchise, which closed its offices at RFK Stadium after the season ended in early July, is about $3 million in debt, according to team sources.

Neither Dizney nor Berl Bernhard, the Federals' chairman of the board, was available for comment last night.

Howard Schnellenberger, who coached Miami to the national collegiate championship last season, apparently will be named coach and general manager of the Orlando team. It would be the second time in four months that Schnellenberger has been hired to coach and operate the Federals.

Sherwood (Woody) Weiser, a Miami hotel developer, signed Schnellenberger to a five-year, $3 million contract in May after agreeing to buy the team. But the sale fell through two weeks ago after the league decided to play a fall schedule in 1986.

According to sources, Weiser posted only a $100,000 deposit, which he forfeited when he did not close on the sale.

The amount of Dizney's down payment was reportedly the last major hitch before the latest contract was executed. Dizney also had offered a $100,000 deposit, but the Federals ownership wanted at least $500,000. Dizney and Bernhard reached a compromise in a telephone conversation late Thursday.

It may be at least another 10 days before the sale can be closed. It is contingent upon Dizney's group receiving league approval for moving the franchise to Orlando, a lease being negotiated with Tampa Stadium and making a deal with John Bassett, owner of the Tampa Bay Bandits, for infringing on Bassett's USFL territory.

None of these factors is expected to be a major hurdle.

When Dizney started negotiations for the team last week, he said he only would be interested in acquiring it if the price were right and he could get Schnellenberger as coach and chief operating officer. He appears to have accomplished both.

One USFL source called the purchase price "a steal." In essence, Dizney is bailing out a failing business. Most of the money he is paying for the team will be paid only if the franchise and the league succeed.