Rep. Michael D. Barnes (D-Md.) didn't have much of a reelection fight this fall, but since his victory he has been busy campaigning -- for a seat on the House Budget Committee.

"He contacted us four months ago," a staff member for Rep. Mary Rose Oakar (D-Ohio) said recently. A deal was struck: Barnes agreed to support Oakar's bid to become the Democratic Congressional Caucus secretary in return for a pledge that she would support Barnes' effort to get on the Budget Committee.

Like dozens of other members of the House and Senate, including several from Virginia, Barnes, who will be entering his fourth term in the House, is jockeying for a spot on a more prestigious committee.

Already a Foreign Affairs subcommittee chairman, Barnes would add the Budget Committee seat to his duties. And he says that under the House rules he can take that assignment and not have to give up his seat on the Foreign Affairs panel or the District committee, which hears many issues related to his Montgomery County district.

Although most committee assignments will not be announced until January, the lobbying has paid off already for one area congressman. Rep. Frank R. Wolf (R-Va.) last week won a seat on Appropriations, one of the most sought-after House assignments. Stephanie Bolick, a Wolf aide, said the Republican Executive Committee on Committees gave Wolf one of three GOP seats on Appropriations.

Wolf will have to give up his assignment to the Post Office and Civil Service and Public Works committees, but Bolick said the Fairfax County congressman, who recently won his third term, believes he can have "a greater impact on matters affecting Northern Virginia" by serving on the money committee.

Rep. Stan Parris (R-Va.) was not so lucky. The House Republican leadership rejected his bid to get on the Ways and Means Committee, the panel that will have a major voice in any rewriting of the tax laws.

While Barnes and Republican Rep.-elect Helen Delich Bentley of Baltimore County are the only Marylanders seeking new posts, a handful of Virginia politicians are working vigorously to switch committees.

Rep.-elect J. French Slaughter, the Culpeper Republican who will represent some of Northern Virginia's outer counties, is seeking a seat on the Energy and Commerce Committee, and Rep. Herbert H. Bateman, a Newport News Republican, is trying once again to win a seat on the Armed Services Committee.

"He barely lost last time so we've got a full-court press going this time," said Dan Beck, a spokesman for Bateman.

The rule of thumb for getting a new assignment is that seniority is the most important single factor. But Rep. Norman Sisisky, a colorful Democrat from Petersburg, was given a plum, Armed Services, when he arrived on the Hill in 1982. Now, entering his second term, he is willing to give it up for the Ways and Means Committee, where about 15 Democrats are vying for, at most, three vacancies.

"I told them the party leadership that I know it would be nice to wait, but at my age I don't have time to wait," Sisisky, 57, said last week. "I want to have my cake and eat it too."

Bentley, who defeated 11-term Democratic Rep. Clarence D. Long, had appealed to the GOP leaders to assign her to Appropriations in her first term, but she was rejected.

If Wolf had failed to win the seat on Appropriations, Virginia and Maryland would have had only Rep. Steny H. Hoyer, a Prince George's County Democrat, on that major committee. Long and retiring Republican Rep. J. Kenneth Robinson of Virginia are veterans of the committee.

Generally, the key to getting prestigious committee assignments comes down to a mixture of geography, personality and political ties.

"It's a lot of behind-the-scenes wheeling and dealing and trading in on your IOUs," said Sue Seiden, Sisisky's spokeswoman. "It's basic lobbying."

Hoyer's telephone, for example, has been ringing incessantly since the election, according to his press secretary, Karin Johanson. Last week, Hoyer was elected one of 12 regional representatives on the 30-member Democratic Steering and Policy Committee, which hands out committee assignments.

"He has talked to a good number of people, much the same thing he did when he wanted to get on Appropriations," Johanson said.

Other potential changes in the committee assignments for the Maryland and Virginia delegations are:

* Republican Sen. Paul S. Trible of Virginia is trying to move to the Foreign Relations Committee. He is currently on Commerce, Science and Transportation and Banking, Housing and Urban Affairs.

* Rep. Thomas Bliley, a Republican from Richmond, would like a seat on the House Permanent Select Committee on Intelligence.