The current Montgomery County school board took its last official act early yesterday morning, going out in the same combative style that has been its trade mark for the last four years.

Over the protest of Superintendent Edward A. Andrews, and despite a rare abstention from their philosophical leader, Marian Greenblatt, conservative members of the lame-duck board flexed their political muscle one last time, approving formation of a citizens advisory committee on employe negotiations that may be dominated by what board liberal Blair Ewing complained are conservative organizations.

Jim Cronin, one of the four incoming board members who are expected to join incumbent Ewing in a new, more liberal board majority, characterized the action as a "last cannon shot across the bow."

The committee, in existence once a decade ago, would advise the board on union negotiations during the budget process. The sponsor, Carol F. Wallace, one of four incumbents whose tenure will officially end next week, said the committee should include a "varied cross section" of organizations, including the Taxpayers League, the Montgomery County Chamber of Commerce, Allied Civic Association and the Montgomery County Civic Federation. She also suggested including representatives of the County Council and county executive, but tried to withdraw them because their presence would be like "putting the fox in the hen house." But those representatives remained in, along with the addition of the Montgomery County Council of PTAs.

Ewing warned it would not be an "auspicious beginning" to approve the measure and unsuccessfully attempted to table it. Finally, after nearly an hour of the kind of sparring and debate that gave it its reputation of feistiness, and a warning from Supt. Andrews that it should not be passed "under any circumstance," four members of the seven-member board approved the measure. Three of them are outgoing members.

The only surprise was the abstention of Greenblatt, one of two remaining members of the current board majority. (In addition to the defeated Wallace and Joseph Barse, the terms of board president Eleanor Zappone and interim appointee Richard Claypoole also expire Dec. 1.) Greenblatt, in a quiet voice, said she did not think it wise for the old board to take action that would affect the new board.

Three new board members, Cronin, Marilyn Praisner and Robert Shoenberg, joined the outgoing board members at the table, where the discussion dragged on until after midnight.

After the meeting, Cronin cried foul and predicted that the new board probably would reverse the decision or not fill the committee.