The House Assassinations Committee has imposed "almost a total blackout" on its work, a key committee member conceded yesterday.

Rep. Richardson Preyer (D-N.C.) made the remark to reporters following a rare public session of the committee in his office yesterday morning.

The only action taken at the open meeting was to empower Chief Committee Counsel G. Robert Blakey and staff lawyers Kenneth Klein and William Triplett to obtain sworn statements from witnesses in the United States and abroad.

Blakey has deliberately - and thus far successfully - muted the controversial investigation into the murders of President Kennedy and the Rev. Martin Luther King Jr. since taking over as chief counsel in June. Public information officer Burt Chardak has left the committee and that post has been abolished.

"It's almost a total blackout," Preyer acknowledged to reporters about the committee's work. He said, however, that he expects the panel will have to make some public announcements by mid-September about the course of the inquiry in order to lay the groundwork for continued funding for next year.

The panel's 1977 budget totals $2.5 million. It has held only two public hearings at which witnesses - underworld chieftain Santo Trafficante Jr. and soldier of fortune Loran E. Hall - refused to testify, invoking their constitutional rights under the Fifth Amendment.

Preyer and Rep. Yvonne Burke (D-Calif.) were the only committee members present at yesterday's brief session. Preyer said, in response to a reporter's question, that committee rules do not require, the presence of a Republican member for an official meeting.