Getting elected was the first step, but the real races -- the jostling among political highsteppers and mudders for key committee spots -- formally began at noon yesterday as the 96th Congress convened.

In reality, few major committee changes are foreseen in the House and Senate, but legislative railbirds already were savoring developments that could affect the tone of this new Congress.

For example:

It seemed likely that Rep. Dan Rostenkowski (D-Ill.) would give up the chair of the Ways and Means health subcommittee in favor of another post. That raised the prospect of a new look toward health in this Congress -- liberals running three of the four congressional health subcommittees.

A long-brewing effort to prevent Rep. Jamie L. Whitten (D-Miss.) from rising to the chairmanship of the House Appropriations Committee emerged publicly.

Beyond these developments is the more basic jockeying -- newcomers and veterans with seniority vying for coveted open seats on the glamour committees that help set Capitol Hill's legislative tone and agenda.

House and Senate steering committees are expected to begin dealing with general committee assignments as early as today, with the Democratic caucuses moving next week into election of committee chairmen.

Once the committees are formally constituted, the fun begins. Except in the case of Appropriations, whose subcommittee chairmen are passed on by the caucus, the committees will pick their subcommittee leaders.

There will be fun in Ways and Means, for starters. Rostenkowski said yesterday that he has almost decided to give up his health subcommittee chairmanship and take over a tax-writing subcommittee that will be given expanded powers.

Next in line for the health job is Charles Rangel (N.Y.), whose more liberal views on such issues as national health insurance and hospital-cost containment cheer the promoters of those slow-moving causes.

A spirited fight has developed for the chair of a counterpart House Commerce health subcommittee, pitting Richardson Preyer (N.C.) against the more liberal Henry Waxman (Calif.).

Both men want the job, which became vacant with the retirement of Paul Rogers (Fla.). Preyer, heir to a pharmaceutical fortune, is being criticized for a possible conflict of interest although he insists he will not, if elected, participate in drug matters.

Waxman is campaigning actively and, according to associates, picked up an additional vote in the close race when Preyer last week spoke critically of the surgeon general's new report on the health effect of cigarettes -- a major product of his home state.The counterpart Senate chair is held by Edward M. Kennedy (Mass.), whose views Waxman generally shares on health insurance and hospital costs.

Meanwhile, a coalition of labor, nutrition and environmental groups, led by Public Citizen's Congress Watch, unveiled its campaign to thwart the conservative Rep. Whitten from getting the Appropriations chairmanship.

The 12 groups sent every House Democrat a packet of material outlining their reasons. They described the Mississippian as "out of step with his party, his administration, his colleagues in the House and his country."

Their preference is Edward P. Boland (Mass.), next in line in seniority. Under the rules, the caucus must reject Whitten before it can consider another candidate.

A more precise test of the congressional leadership's intentions will be how it determines that vacancies on the key committees are filled -- whether liberal replaces liberal, whether close balances are retained.

Senate Majority Leader Robert C. Byrd (W.Va.) won approval yesterday to move quickly this week on committee assignments. Sens. John Culver (Iowa), Howard Metzenbaum (Ohio), John. Stennis (Miss.), Robert Morgan (N.C.) and Daniel Patrick Moynihan (N.Y.) were named to the Democratic Steering Committee, assuring an identical ideological belance with its predecessor in the 95th Congress.