House Democrats yesterday doled out committee assignments for the 99th Congress, with most plums going to lawmakers backed by heavy hitters in the House, and yielded to Republican pressure to increase the number of GOP seats on most major committees.

The assignments to every committee except Rules and intelligence were made during an all-day, closed meeting of the Democratic Steering and Policy Committee, a group of 31 Democrats that includes the entire House Democratic leadership. The assignments must be approved by the Democratic caucus next week.

The most coveted vacancies were on the Appropriations, Ways and Means and Budget committees.

House Speaker Thomas P. (Tip) O'Neill Jr. (Mass.) won two of the plums for his home state: Rep. Brian J. Donnelly (Mass.) was easily selected to fill a vacancy on Ways and Means, and freshman Rep. Chester G. Atkins (Mass.) was given a seat on Budget.

Majority Leader James C. Wright Jr. (Tex.) got Texans on Appropriations and Budget -- Reps. Ronald Coleman (Tex.) and Marvin Leath (Tex.) respectively -- but was unable to swing a seat on Ways and Means for Rep. Michael A. Andrews.

The only other Democrat appointed to Ways and Means was Rep. William J. Coyne (Pa.), who had been pushed by Rep. John P. Murtha (Pa.), one of the best deal-makers in the House.

And the only other vacant seat on Appropriations went to Rep. Richard J. Durbin (Ill.), who was backed by Ways and Means Chairman Dan Rostenkowski (Ill.).

In addition to Atkins and Leath, the other Democratic lawmakers appointed to the Budget Committee were Reps. Charles E. Schumer (N.Y.), Barbara Boxer (Calif.), Michael D. Barnes (Md.), James C. Slattery (Kan.), Buddy MacKay (Fla.), Marty Russo (Ill.) and Ed Jenkins (Ga.)

Democratic officials said yesterday that the large number of new Budget Committee members, the result of rules limiting service on the panel to six years, would not have a dramatic effect because, more than any committee, Budget takes its cues from the Democratic leadership.

Most vacant seats on other committees were filled with freshmen.

Republicans are scheduled to parcel out most of their committee seats today. Although Congress officially convened Jan. 3, both parties waited until this week to make assignments because Democratic and Republican leaders had not agreed on party ratios for each committee.

For the last few years, the GOP had accused the Democratic leadership of trying to keep firm control of key panels by denying Republicans fair representation on them.

Recently Republicans suggested that they would boycott committee meetings to make their point and embarrass the Democrats.

But GOP officials said the confrontation appeared to have been defused by an agreement between Minority Leader Robert H. Michel (R-Ill.) and Majority Leader Wright to increase the Republican proportions on every committee except District of Columbia, House Administration and Rules.

According to one Democratic official, the Democrats yielded to avoid confrontation and keep from being left "open to charges of unfairness."

Republicans would still not have as many seats on the "money" committees -- Appropriations, Ways and Means and Budget -- as their numbers in the House would imply, but Democrats agreed to reduce their majorities there.