President Carter's subordinates are misusing federal power and federal funds to "buy" his renomination, seven supporters of Sen. Edward M. Kennedy, Carter's leading opponent, charged yesterday in a lawsuit filed in U.S. District Court.

The subordinates -- seven members of the White House staff and seven Cabinet secretaries -- have engaged in "a concerted course of conduct" that "threatens the integrity of our democratic system of government and debases the election of the highest public official in the land," the suit alleged.

Tim Smith, counsel for the Carter-Mondale Presidential Committee, said the suit appears to be "mainly politically motivated and has as its aim some harrassment."

The conduct attacked in the suit centers on use of "the public treasury for salaries, travel expenses, costs of meetings and other political outlays," the granting and withholding of federal jobs "based upon political support by the employe," and the promise and award of federal programs and funds to communities "as political inducements and rewards."

Such allegations have been made in connection with renomination or reelection campaigns of presidents down through history. Ironically, some of Carter's critics, including many Kennedy supporters, have complained that he has been insufficiently bold in asserting the powers of his office.

But the suit is reportedly the first in which members of a president's own party who support a challenger allege major violations of the Constitution, including the guarantees of freedom of speech and the equal protection of the laws.

In addition, the scale of the purported violations was stressed at a press conference by Joseph L. Rauh Jr., one of three attorneys who prepared the complaint. "I have never seen this much use of federal funds and federal power," said Rauh, a veteran of Democratic politics and former chairman of Americans for Democratic Action (ADA). At the same time, he acknowledged, most Democratic presidents haven't faced serious renomination challenges.

The three lawyers "have no question in our minds and hearts that this is a serious suit," Rauh said. The others are his partner, John Silard, and William A. Dobrovir, and expert on election litigation.

The principal plaintiff is William W. Winpisinger, president of the International Association of Machinists, AFL-CIO. The Machinists Non-Partisan Political League, of which Winpisinger is co-chairman, is paying the costs. Other plaintiffs include ADA President Patsy T. Mink and Vincent L. Connery, president of the National Treasury Employes Union.

The accused subordinates include secretary of the Cabinet Jack Watson, White House Chief of staff Hamilton Jordan and presidential press secretary Jody Powell. The Carter-Mondale Presidential Committee is also a defendant.

The nomination contest will be under way in earnest in a few weeks. On Jan. 21 in Iowa, delegates will be elected in caucuses. From February to June, primaries will be held in 34 states.

Because of this schedule, the lawyers told reporters, they will ask the judge to whom the case was assigned, June L. Green, to order the taking of depositions and other pretrial proceedings to begin in a few days -- even before the defendants file answers. Rauh indicated that he wouldn't make an issue of representation of individual defendants by the Justice Department despite its use of public funds.

The suit asks Judge Green to rule that the defendants' conduct violated the Constitution and federal laws and to enjoin them from:

Being paid out of public funds for time spent in normal working hours on activities, such as speeches and press conferences, for the benefit of the Carter candidacy.

Claiming advance payment or reimbursement from the federal treasury for expenses incurred in travel undertaken for the candidacy, or "scheduling official travel to coincide with their Carter campaign travel plans."

Making support of the candidacy a condition of federal employment, making "patronage" the basis of jobs in the 1980 census, or "awarding any federally funded benefit or project as reward for the support of any person for the Carter candidacy."

The suit noted that federal funds to Detroit were increased after Mayor Coleman Young endorsed Carter and that federal funds to Chicago were cut after Mayor Jane Byrne endorsed Kennedy.

Attached to the complaint is a stack of news stories and other exhibits purporting to show that the defendants have engaged in just such allegedly unconstitutional activities.

The suit cites, for example, a statement by Jordan in October that federal employes not barred by law from political activity are expected to campaign for Carter -- and will be dismissed if they campaign for Kennedy.