Washington Redskins owner Jack Kent Cooke and the D.C. Armory Board have all but finalized an agreement for a new football stadium that will keep the Redskins in the District, sources said yesterday.

"Conceptually, that deal has been worked out," a source familiar with the negotiations said.

"There is no letter of agreement," another source said, "but things are very, very close to being put together."

The source familiar with the negotiations said the stadium, to be built on what is now RFK Stadium's Parking Lot 6, will have a seating capacity of 72,000 to 78,000, including 365 skyboxes.

The nearby Langston Golf Course will be "minimally disturbed" by the new facility, the source said.

In addition, the source said Cooke ultimately will repay the District for all capital improvements associated with the new stadium. "It will not cost the city taxpayers a penny," the source said.

Cooke could not be reached for comment yesterday. Mayor Marion Barry's office declined comment.

Cooke has said previously he would build the stadium with his own money, but it has been believed the District would be financially responsible for such infrastructure items as sewer and water lines, lighting, road improvements and parking. The District still will be reponsible for making necessary improvements.

Cooke would like the Redskins to begin playing in the new stadium at the start of the 1993 season, but the source said "they might not get there until halfway through the '93 season." The club's lease for RFK Stadium will expire after the upcoming season, but an extension will be made "simultaneously" with the conclusion of the agreement for the new stadium, the source said.

"There's no problem" with an extension of the RFK Stadium lease, the source said. "Everything has been very cordial with Mr. Cooke."

It is believed Cooke's relationship with Barry and the armory board's other members, Maj. Gen. Calvin G. Franklin of the D.C. National Guard and businessman Stuart Long, will prompt Cooke to try to close the deal before the board's membership changes. Barry, whose term as mayor will expire at the end of the year, has said he will not seek reelection.

There also may be fewer problems with winning approval for the new stadium than there had been because the sources said the Langston Golf Course will not be reconfigured and the Anacostia River will not be filled in.

A proposal that involved filling in a portion of the river prompted environmental concerns, and a proposal that involved using part of Langston's current layout for parking aroused oppositon from patrons of the course and local residents.

"They're not going to do much to Langston," the source familiar with the negotiations said. "They might use the driving range for parking on game days, something like that, but they are not going to do any plowing or anything like that."

Of filling in a part of the Anacostia, the other source said, "The issue has been dropped for a long time."

There are environmental impact studies that will have to be filed with, and approved by, the Interior Department. Studies have been conducted to be sure the project is viable, said a source who called them "much more than preliminary."

There has been a wetlands study and a study of the new facility's impact on the Anacostia River, the source said.