The American Agriculture Movement's police-enclosed encampment on the Mall dwindled yesterday as some of the protesting farmers quietly began exiting Washington after they failed once again to win sympathy from the Carter administration.

No precise count of the departing farmers could be obtained yesterday, but many of those leaving claimed they would be replaced by their neighbors and predicted many farmers will remain here to press their demands for higher farm prices.

"I got a wife, a kid, a bunch of hungry cows and a sick daddy back home and I got to get back," said Darrell Haynes, a Cullman, Ala., farmer, who drove out of Washington, leaving his tractor on the Mall with a friend.

D.C. Police said that as of yesterday 85 of the 625 tractors the farmers once had on the Mall had departed. While the departing tractors were being escorted to the Virginia line by police, a group of the movement's leaders met with Agriculture Secretary Bob Bergland.

And Bergland, who said Tuesday that many of the protesters were motitivated by "greed" refused to budge from his opposition to their demands for higher farm prices.

Park police voiced renewed concern yesterday about the Mall encampment and said the farmers may have done as much as $500,000 damage to the area. George Berklacy said the tractors have destroyed 25 trees, seriously damaged the Mall's underground sprinkler system, and ruined much of its new sod.

Berklacy said police still have no idea when the remaining farmers might leave.

About 100 tractors left the Mall at 10:25 a.m. yesterday for another parade around town. The farmers stopped their tractors near the American Farm Bureau building at 425 13th Street NW and 150 farmers barged inside, past protesting secretaries. Police said the farmers burnt holes in the carpet and accused the bureau, which claims 3 million members, of "not representing farmers."

The tractors left the bureau 20 minutes later and stopped at the Agriculture Department, where three tractors were driven up to an entrance, forcing federal workers to climb over the tractors when leaving or entering. After about 30 minutes, the farmers drove back to the encampment that many call their "pen."

Police assigned to the Mall yesterday had a playful snowball fight with the farmers and several policemen walked around the area, sporting the baseball caps of the Agriculture Movement.

"These farmers are probably the best protesters we've ever had come to town," said D.C. policeman Roger P. Jones, who rode around in a tractor yesterday with "Donna from Illinois."

Gerald McCathern, one of the protest leaders who met for an hour and a half with Bergland yesterday morning, said later at a press conference that Bergland recognizes "we represent the grassroots farmers."

Tom Sands, an aide to Bergland, said the meeting was "polite and civil," but repeated that Bergland does not consider the American Agriculture Movement, with its demands for "90 percent parity," to be representative of small farmers in the country.

Sands said Bergland "rejects the term parity" and has no intention of raising parity to 90 percent. Parity, which farmers say amounts to a fair return on their labor and investment, is supposed to give the farmer the same relative purchasing power as farmers had in the boom years of 1910-14.

Inside the police barricades, Tom Letcher, a farmer from Christian County, Ill., waited for a friend to return with his tractor and said he was leaving Washington at 5 p.m.

"Psychologically, this trip here has been good for everyone," Letcher said. "It makes us feel we're all done something to preserve our way of life."

At motels and hotels in the Capitol Hill area yesterday, farmers crowded around front desks, checking out and grumbling about the "ridiculous" cost of staying in Washington.

Duane Rushing, a farmer from Medill, Okla., shared a singie room at the Quality Inn on Capitol Hill for four nights and paid a bill yesterday for $290. "I just can't afford to stay around here at those prices," Rushing said.

He said it took him "about one day" in Washington to start worrying about "my cattle and my wife." Rushing, who also came to Washington last year, said it was easier to stay in the city this time because the sight of the tractors on the Mall kept him from getting homesick.

Some farmers, tiring of the routine of tractorcades and visits with their congressional representatives, have begun touring the museums that surround them on the Mall.

Hershell Essary, from Floyd, N.M., said he found some of the paintings in the National Gallery of Art "very pretty," but added that he thought it a "waste of government space" that their were not any desks and office workers in the gallery's large hall-ways.

In the Skyline Inn on South Capitol Street, which has served as the farmers' headquarters for the last 10 days, Basil Dowes said he was anxious to get back to Copeland, Kan. "You bet I'm tired, my feet are about wore out," Dowes said. "No sir, you couldn't pay me enough to live in this town."