Berl Bernhard, a prominent Washington attorney, has replaced Cincinnati businessman Marvin Warner as the prospective owner of the Washington franchise in the proposed United States Football League.

Organizers of the USFL say they are not ready to formally announce the founding of the league, which is scheduled to start play in the spring of 1983 (its proposed sesaon would run from March through June). They are waiting first for prospective owners to each post a $1.5 million letter of credit by April 12.

Bernhard, a partner in the firm of Verner, Liipfert, Bernhard and McPherson, said he will decide sometime before the April 12 deadline whether he will own the Washington team. He said he was "quite interested and very serious" about the venture, which hopes to use RFK Stadium for home games.

"I have to go over quite a bit more of the information about the franchise," he said, "but I'm intrigued. I think there is a market for another team, especially in the spring, which is a great time in Washington. We wouldn't have a significant competitive sport to fight in the spring and I think there is room for another pro football team besides the Redskins."

Bernhard was recruited by Warner, who has decided to sponsor the proposed franchise in Birmingham, Ala., his native city.

"I had talked with Marvin about this the last few months," Bernhard said. "Then I saw him in Geneva last week and that was the first time it was clear he was going to take Birmingham. That's when I seriously began considering my position . . . I'm inclined to think it would be safer to get other people involved with me but I haven't figured out the entire (financial) package yet.

"I know there are other people interested in having the Washington franchise, so I want to make my final decision quick enough to leave time in case I decide not to go ahead. I don't want to deprive Washington of a franchise."

Bernhard, 52, was general counsel and a director of the Evening Star Co. when the paper was owned by Joe Albritton. He was director of the U.S. Commission on Civil Rights under John Kennedy and a senior aide to Edmund Muskie when he was secretary of state. He also was campaign manager for Muskie's unsuccesful bid for the presidency in 1972.

One problem Bernhard might encounter is with the RFK Stadium lease. Warner switched to Birmingham in part because the Armory Board would not let him keep proceeds from concessions.

Bernhard said the stadium lease was one of the areas he still needed to explore.

Peter Spivak, the present league chairman, said there will be at least 12 franchises in the league. But, he said, "I would hate to not have a team in Washington. I'm sure we will have one there. We want one and I can't imagine having a successful league without a club in the nation's capital."

Prospective league owners will meet next week to formally adopt permanent bylaws. Stadium contracts will have to be signed by May 20. By then, Spivak said, he hopes the league will have hired a commissioner. Interviews for that position have begun, he said.

Besides Washington, the USFL hopes to have teams in New York, Philadelphia, Chicago, Detroit, Boston, Tampa Bay, Memphis, Los Angeles, San Francisco, San Diego and Houston. The league eventually hopes to tap the lucrative cable network market, which has limited sports offerings in the spring.