If Houston Astros owner John McMullen decided to move his troubled franchise to Washington, he would face a maze of complex legal hurdles, the biggest being breaking a stadium lease that runs through 2002.

McMullen, who has seen the Houston franchise's attendance decline steadily since 1980, told The Washington Post Thursday he is unhappy with the team's situation in Houston, but that "I won't know anything until the end of the year."

However, several sources say McMullen is seriously considering relocating the franchise in Washington for the 1987 season, and already may have decided to do so.

The Astros have lost an estimated $10 million the last five seasons, and their attendance has fallen almost 50 percent since drawing 2.2 million in 1980.

Among the obstacles McMullen must overcome is a 40-year lease the city and the franchise signed in 1962. City attorneys in Houston yesterday were trying to determine how binding the lease is.

One source in the city administration said that if McMullen tries to move the team, he would at least have to pay damages to the city and perhaps would be forced to stay.

Another man who has seen the lease said, "I'm certain there's a performance clause in it that says there must be a team playing in the Astro dome for the length of the lease. Unless baseball plans to move another team in there, that might be tough to get around."

An additional obstacle may be that any franchise relocation must be accompanied by 75 percent approval of the owners in the team's league and majority approval by the owners in the other league.

McMullen said that, if he were going to move his team, he would do so within the framework of Baseball's Long Range Planning Committee, of which he is a member.

Ed Durso, a major league baseball executive vice president, reiterated yesterday that Commissioner Peter Ueberroth frowns on franchise shifts and has proved it by working to put together a group to keep the Pirates in Pittsburgh.

"You're not going to find a franchise lower than that one," a former National League executive said.

"I don't even see the Houston and Pittsburgh situations being comparable. The Pirates were so much lower, and the commissioner made it clear he didn't want the Pirates to leave."

Durso said: "The commissioner is interested in franchise stability. If a team did want to relocate, we'd look at any number of criteria."

Durso also said that if an owner wanted to move without permission, "We feel we'd win" whatever legal action was taken.

One management source said he doesn't think McMullen "can get the permission unless Houston was going to get another team. I think before the owners would approve relocation, he'd have to try to sell the club to a Houston group and there are people down there who'd buy it."

McMullen was unavailable for comment yesterday, but in an interview with a Houston reporter refused to back off his earlier statements that he is unhappy with attendance in Houston.

He again said he had not spoken to anyone with the D.C. Baseball Commission about moving the Astros and said he was doing everything he could to make the team's marriage with Houston work.

That marriage is a complex one and also could haunt him if he wanted to leave, Houston sources said.

As owner of the Astros, he is also a major shareholder in the Houston Sports Association, the governing body of the Astrodome.

In 1984, McMullen reported the Astros lost $5 million, but that his interest in HSA had made $3 million, for a net loss of $2 million.

His case to baseball will be that he has given the city a decent team, heavily marketed the area and still not been able to attract enough fans to make money.

Yesterday, at least one Houston government official said he could sympathize with McMullen's problems.

"He's not been getting much support in Houston from a pure business sense," said Judge John Lindsay of the Harris County Commissioners Court. "If they start winning, I think attendance will go up . . . This is not a community that supports losing. If you put yourself in his shoes, you can see where, if he could make the move, he has a lot to gain."

Harris County recently completed a $40 million renovation of the Astrodome and its surrounding buildings, the Astro Hall Convention Center.

Another $500 million bond program was supposed to go before county voters early this year but, because economic conditions were so bad, the Commissioners Court decided to wait until this summer to send it before the voters.

That package would spend another $53 million on improving the interior of the Astrodome.

"Needless to say, we'd be very disappointed if they chose to move and would do everything within our power to get them to stay," Lindsay said.

James Dalrymple, general manager of RFK Stadium, said yesterday the stadium could be ready for play by next season, but it would be a rush.

"If we know something in a reasonable amount of time, we'll get the stadium ready," he said. "But it would take a lot of work and money."

The biggest problem at RFK is rearranging the stands in a baseball configuration. The stadium has been in a football configuration for more than 10 years, and the once-moveable bleachers that created a baseball diamond's left field area are rusted in place and in several inches of soil.

Another possible snag could be the transfer of title for RFK from the Department of the Interior to the District government.

A source said until that occurs, the city would lack flexibility in negotiating with a potential tenant.

However, Washington Mayor Marion Barry has indicated working out a lease would not be an obstacle to getting a team.