The governors of Virginia and Maryland met at Mount Vernon yesterday and agreed to fight a weed.

Virginia's Gerald L. Baliles and Maryland's Harry Hughes chose George Washington's home as the place to sign an interstate compact pledging to cooperate in the fight against hydrilla, an aquatic weed that has spread rapidly in the Potomac River during recent summers.

"Today, we take up the issue of hydrilla: George Washington would be proud of that," quipped Baliles as he opened the third day of a "work week" in the Washington suburbs.

Since it was introduced into the Potomac River a few years ago, hydrilla has spread so rapidly that Baliles joked that some people think the aquatic weed is "a genetically deformed gorilla."

Hydrilla has spread from 10 acres south of the Woodrow Wilson Bridge in 1982 to 1,900 acres last summer, sprouting thick, impregnable roots just below the surface that create an impassible barrier for boats.

The Army Corps of Engineers has said that under the Clean Water Act, hydrilla can be treated either mechanically or chemically. But Baliles said that Virginia, Maryland and District officials have ruled out using chemicals because of environmental considerations.

Baliles, who will help dedicate an extension of Metro's Orange Line to Vienna this morning, also met yesterday with Transportation Secretary Elizabeth Hanford Dole to urge more federal funding for Metro; went to the District Building, where he told Mayor Marion Barry he supports the city's efforts to secure a major league baseball franchise and the Democratic Party's 1988 convention, and discussed trade relations with Ambassador Kyung Won Kim at the South Korean Embassy.

At Mount Vernon, the governors also agreed to continue restrictions on catching rockfish, also called striped bass, while a restocking program is under way, and to study ways to restrict private boat owners from using marine paints containing pesticides that ward off barnacles but harm such aquatic life as oysters and crabs.

At a news conference, Hughes criticized a recent Washington Post article that detailed the two states' efforts to police pollution in the Chesapeake Bay. He said that the article used outdated figures, and he expressed concern that the public may be expecting too much, too soon from the state and federal cleanup of the bay.

"That effort is not a matter of a week or a month or a year, but of a decade," Hughes said.

The Maryland governor said that since the Save the Bay effort was announced in 1983, Maryland has stepped up its enforcement efforts against commercial and governmental polluters by nearly 50 percent. He said that runoff from farms and city streets poses more of a pollution problem in the bay than toxic chemicals and metals disposed of by industries and sewage plants.

Baliles, who was Virginia's attorney general from 1981 to 1985, said he believes "there is always room for more enforcement in cleaning up rivers and streams, as well as air. There's room for improvement."

The governors reaffirmed their commitment to constructing the full 103-mile Metro system but, after his meeting with Dole at DOT headquarters, Baliles was pessimistic.

"The federal level of support is not likely to be there in the future," Baliles said.

Baliles said he had argued that the federal government "took the lead in urging the states to participate" in Metro "not only as a demonstration project, but as transportation for the nation's capital, where federal employes are involved in the congestion."

Dole is "a very good advocate for the administration's position that they face serious financial problems at the federal level," Baliles noted, but said he had pointed out that the federal government is involved in "a contractural commitment honored by all the other parties."

The governor, who took office Jan. 11, told reporters and editors at The Washington Post that he has found his job to be everything he expected, and added that he is not troubled by frequent comparisons to his celebrity predecessor, Charles S. Robb. Baliles said that he never has compared himself to Robb, the son-in-law of the late president Lyndon B. Johnson.

"I knew what I wanted to do," Baliles said of his first four months in office.

Asked if he was joining other Virginians who have been championing Robb as a Democratic presidential candidate, Baliles replied: "Has he announced yet?"

When pressed, Baliles said that he will endorse Robb, "if he announces."

The governor also expressed confidence that Congress will approve the sale of National and Dulles International airports to a regional authority.

"If it doesn't fly this year," Baliles said of the proposed sale, "it is unlikely to go."