The Federal Trade Commission has volunteered to cut its budget by 10 percent across the board this year and next in appeal to the Reagan administration to preserve its antitrust role.

Responding to a White House budget directive that would gut its antitrust operation, the commission warned in a letter that the proposed cuts would force the agency to fire up to 250 employes -- one-seventh of its total work force.

The plea, in a letter to David Stockman, director of the Office of Management and Budget, appeared to be as much of an appeal for help from Congress, however.

The result of the cuts would be "disasterous" and might force the agency to end pending cases, the FTC said, accusing the Reagan administration of a "short-sighted effort to effect an extremely small savings of short-term budget dollars."

Further, the commission said the plan would force the agency to cut this year's budget by $6.36 million, a reduction of 37 1/2 percent for the remaining six months of the fiscal year.

The cuts would require ending cases in litigation, and the FTC's Bureau of Competition would be operating at "one-half of its current level" by Oct. 1, if the cuts were adopted by Congress, the FTC said.

The letter -- signed by all five commission members, three Democrats and two Republicans -- made a strong plea for retention of FTC antitrust authority. It is a response to an unprecedented effort by OMB to use the budget process to alter the policy-making role of an independent regulatory agency.

Throughout the letter, the agency stressed that the commission is basically a creature of Congress, an obvious appeal for support from its congressional constituency.

The letter was distributed widely on Capitol Hill yesterday amid growing congressional concern about the FTC budget cuts. Rep. Benjamin Rosenthal (D-N.Y.) previously announced that a subcommittee he chairs will hold hearings on the FTC cuts and on a 30 percent proposed cut in the budget of the Consumer Product Safety Commission.

The FTC letter noted that previous government studies have concluded that both the commission and the Department of Justice should continue to share antitrust responsibilities, as they have since the 1913 enactment of the Clayton Antitrust and Federal Trade Commission acts.

"In our judgment, these decades of settled practice ought not to be set aside on the basis of an executive budget decision without careful study of its law enforcement impact, without public debate, and without the scrutiny of the congressional committees directly responsible for oversight of the pertinent substantive issues," the FTC members wrote.

An aide to Sen. Robert Packwood (R-Ore.), chairman of the Commerce Committee, said that the committee's staff is studying the proposal and that the panel will hold hearings later this year on the antitrust issue.

In last year's debate about the FTC's reauthorization legislation, Commerce Committee members pledged to study the FTC's antitrust powers in oversight hearings. Sen. John Danforth (R-Mo.), a member of the Senate Commerce consumer subcommittee, yesterday said he is "reluctant" to strip the FTC of its antitrust authority.

"My view is that having promised hearings last year, that's the way we should proceed," Danforth said. "You don't do it by hacking away at the budget."

The administration proposal would cut the budget of the FTC's Bureau of Competition by $6.36 million this year and by $16.55 million in 1982 from the Carter administration's proposed budget. The bureau would be "phased out" over 36 months, and the commission's 12 regional offices also would be shut down.

The current FTC budget is $77.9 million, although the OMB recommendation would reduce the agency's budget to $41.8 million by fical 1985. r

But the FTC also said that requiring over 200 employes to be "discharged" before the end of the current fiscal year and over 300 by the end of fiscal 1982 "would have disastrous effects" on the agency's operations.