Promising a vigorous defense of the mission of the Federal Trade Commission before Congress, Acting FTC Chairman David Clanton pledged to improve the agency's relations with Capitol Hill while at the same time working closely with the Department of Justice to clarify antitrust enforcement responsibilities.

Clanton, formerly named acting chairman of the FTC this week, faces potentially difficult budget negotiations with Congress this month and a rash of legislative studies of the commission's consumer protection and antitrust responsibilites.

Although the Reagan administration had proposed deep cuts in the FTC's budget and a three-year phaseout of the agency's antitrust role, that proposal apparently has been scrapped. But Clanton said the administration still is going to ask Congress to phase out the agency's regional offices.

"Our position still remains the same," Clanton said, nothing that in response to the budget proposal of the Office of Management and Budget, the FTC had said that cutting the budgets would limit sharply the FTC's powers. "The cuts hurt; they're deep," he said.

But Clanton, noting that the agency would propose cuts "across the board," said details of the agency's budget proposals would not be released until a congressional hearing next week.

A Michigan Republican, who was a Senate staff member before being named to the FTC five years ago, Clanton, 36, in his first meeting with reporters since his appointment, provided a careful look at FTC rule-making activities, some of which had been the subject of congressional criticism.

Clanton said that he and other FTC members should share "collective blame" for "putting too much emphasis on a few issues." As examples, he cited in particular the FTC's rule-making on advertising directed at children.

But Clanton also said the agency had not received enough credit for moving to adopt cost-benefit analysis and other measures to improve its regulatory processes.

Although he said that he had not been in contact with administration officials about his appointment or his views on the FTC's future, Clanton generally sounded Republican themes, noting the importance of cost-benefit analysis and "general consensus of restraint in the regulatory area."

Clanton said he hoped to initiate discussions with the Department of Justice about their shared antitrust responsibilities. He said that new guidelines for business on mergers might be timely.

Clanton said he hopes to decide soon on commission personnel matters and added that he is "interested and willing" to leave open the possibility of taking on the chairmanship of the agency when the administration decides to name a full-term chairman.