The House Assassinations Committee was chided yesterday for its habit of holding unannounced secret meeting in violation of its own rules.

Rep. Charles Thone (R-Neb.) protested the practice at the outset of what had been billed by Chairman Louis Stokes (D-Ohio) as an "important private informal meeting" of the 12-member committee.

Capitol Police were instructed by a committee staff worker at one point before the meeting to keep the press out, but a Washington Post reporter insisted on taking a seat.

Thick briefing books concerning the committee's investigation into the murders of President Kennedy and Martin Luther King Jr. were distributed to each member, but reportedly the session was called primarily to discuss the committee's search for a new chief counsel to replace former counsel and staff director Richard A. Sprague.

Citing the meeting Stokes had sent Thone said that "of course, this violates the rules of our own select committee."

Those rules, he said, clearly state that "each meeting . . . shall be open to the public" unless and until the committee votes to move into closed session to discuss sensitive matters. The Assassinations Committee's habit of holding informal, secret get-togethers, Thone said, also skirted the requirement that public notice be given of all committee meetings, including those that wind up in closed session.

Urging an end to the practice, Thone said he felt strongly that "the more open we are, the better off we are going to be."

Rep. Harold S. Sawyer (R-Mich.) the newest member of the committee, said he "could not disagree more." He voiced fears over the release of raw, uncorroborated information.

Rep. Yvonne Burke (D-Calif.) said she generally favored open meetings, but found herself in a peculiar position concerning the assassinations inquiry. A number of colleagues in the House, she said, have been contending that the committee ought to keep "all our meetings closed." But she said she agreed with Thone that the proper procedure ought to be followed.

The committee then voted 6 to 1 on a motion by Rep. Samel L. Devine (R-Ohio) to go into closed session. No reason was stated.

Later, after the press was excluded, it was learned that the committee voted to have the official stenographer leave the meeting so that there would be no transcript of what was said. Finally, after briefing the members on the progress of the two investigations, the committee staff was asked to leave. The panel apparently has yet to settle on a replacement for Sprague.