In what appears to be an unprecedented move, top staff members of the Federal Trade Commission have been screening potential candidates for a seat on the five-member agency.

FTC chairman Michael Pertschuk yesterday confirmed that he and key staff members have begun talking to possible candidates to succeed commissioner Calvin J. Collier who is to leave the FTC at the end of the month.

Although some of the potential candidates have complained that they are somewhat offended the process, pertschuk defended the procedure as a "service" to the White House.

"It's quite an open process," he said. Although he has told the White House he will not have "a" candidate, he said he was assured of an opportunity to make his views known and considered before the final selection is made. The process now in progress is an attempt to advise the White House, he said.

"To help them, we've agreed to talk to people and furnish names and reactions to people who are candidates," Pertschuk said.

After Pertschuk interviews the candidates, they may walk to key staff people if time is available. The staff involved include Competition Bureau Director Alfred F. Dougherty Jr.. Consumer Protection Bureau Director Albert H. Kramer and General Counsel Michael N. Sohn. Pertschuk said.

"The purpose of this is to find out more about these people and to pass it on the White House, he said. "We're not taking votes on these people; we are trying to filter them."

It is standard procedure for the White House to solicit the views of the sitting chairman of a regulatory agency on prospective members, even sometimes granting a chairman veto power over candidates. But while it is common practice for a chairman to talk with a candidate before an appointment is made, Washington observers could not recall any instances where the staff of an agency "interviewed" prospective appointees.

"I would think it would put the prospective nominee in a very difficult position," the former chairman of one regulatry agency said yesterday.

Besides the awkwardness of the situation - the staff will ultimately have to live with whoever is selected, and will have to seek his or her votes on matters - one lawyer said the procedure may risea prejudgement question.