The future of a plan to dispose of sludge produced in the District of Columbia remained in doubt last night after King George County, Va., officials revoked early yesterday a permit to build a sludge composting plant there.

The permit had been issued to Dano Resource Recovery Inc. with which the District signed on Tuesday a five-year, $20 million contract under which 800 tons of sludge a day was to be converted into compost.

In an interview last night, Reginald Hayden, chairman of the King George Board of Supervisors, said the plans submitted to two other agencies differed from those submitted by Dano to the county.

Hayden said plans submitted to state and federal agencies showed a 9 1/2-acre site designated as a "spoil area." Spoil is material removed in excavation or dredging.

No such spoil area was indicated on plans submitted to the county, Hayden said.

Plans for the spoil area show it to be "a fairly major undertaking," said Hayden, who described it as "something we'd definitely want to look at" before approving an overall proposal.

Dano executive Henry Valentino said the spoil area was designated on plans sent to the Army Corps of Engineers in response to a question about disposition of dredged material. He said that no such question was asked by county officials and that all the county's requirements were met.

Valentino said Dano hoped to "explain the misunderstanding" and he called the revocation "temporary."

The permit controversy calls new attention to the problem of sludge disposal, a major Washington area issue. The city has been disposing of sludge, the residue of sewage treatment, by burying it at suburban sites. As these sites have been exhausted, the city has come under federal court presure to find other disposal means. The Dano contract was seen as such a means.

In a brief interview last night, Herbert L. Tucker, the city's environmental services chief, said the status of the Dano contract is "the same as always." He said he had not been told of any permit revocation.

In another development, a source in the office of Sen. Patrick Leahy (D-Vt.), head of the Senate D.C. Appropriations subcommittee, said both Virginia senators had expressed concern about the project in a letter to Leahy.

Sens. Harry F. Byrd Jr. (I-Va.) and John W. Warner (R-Va.) as well as Sen. Richard S. Sckweiker (R-Pa.) reportedly asked Leahy to consider actions that "would stop the contract process."

According to the source, Leahy had no intention of trying to interfere in the contract process, and agreed to do "no more or less" than help answer questions raised by the senators.

Under the agreement with the District, sludge from the Blue Plains sewage treatment plant was to be shipped daily by closed barge about 40 miles down the Potomac River to King George for conversion into compost, which is used to condition and fertilize the soil.

Dredging the river would be required to make possible the entry of the barges into a closed building for unloading the sludge.

One concern reportedly raised in the senators' letter is the fate of bald eagles, said to nest near the proposed plant site.

Valentino said last night that the proposed plant would be about three miles from the nearest eagle nests, and would in "no way" endanger them.

In addition to the 800 tons of sludge, plans call for shipment of about 900 tons a day of solid waste to the composting plant, Valentino said. He said no contract for the solid waste has been signed.