The Prince William County School Board selected new leaders last night in a move that some members described as a major compromise aimed at ending the bitter feuding that has beset the board for nearly three years.

Gerard P. Cleary and Maureen Caddigan said their selection as chairman and vice chairman signals a new era of cooperation on the board timed with the arrival in two weeks of a new superintendent for the 38,000-student school system.

Nonetheless, some board members and school observers grumbled privately that the choices of former rivals Cleary and Caddigan symbolize not so much a new era of good feeling as a continuation of the political maneuvering and deal-making in which the board has specialized.

The vote on Cleary was 4 to 3; on Caddigan, it was 7 to 0.

The selections were announced in an unusual news release on Tuesday, more than 36 hours before the board's vote. Caddigan said at the time that she hoped the votes would be unanimous, and that they represented a compromise between two factions that have clashed sharply on issues ranging from the leadership of Richard W. Johnson, the outspoken and colorful superintendent fired by the board last year, to questions of student discipline and teacher pay.

"He and I have not really gotten along very well over the past couple years," Caddigan said of the new chairman. "We wanted to show that we could bury the hatchet."

In the past the board has been so fractured that even some of its members acknowledged it has a reputation in the community as narrow-minded and peevish.

Some school observers said the one-year elections of Cleary and Caddigan are not a compromise among the divided groups, but a reshuffling of the factions. The selections followed a stalemate in which three board members threw their support to board member Patricia L. Cusey, and three backed veteran member George P. Mullen. Only Cleary had not committed to a candidate, according to other board members.

Cleary apparently decided that the ideal way to break the deadlock was to install himself as chairman in an alliance with his old foes, who had supported Mullen.

Cleary, who served as chairman from 1980 to 1986, said last night that he is returning to the post not out of personal ambition but because of a desire to "unite the board." Caddigan has often crossed swords with Cleary since she joined the board in 1984.

By last fall, the dissension on the board had become so severe that what ordinarily would have been a routine vote to approve the minutes from a previous meeting degenerated into a squabble that lasted an hour.

Many of the board's debates, however, are far from petty. Prince William's school system -- the second largest in Northern Virginia, after Fairfax County's -- is grappling with a student population that is rising fast and parent expectations for quality that are rising even faster.

This spring the board named Edward Kelly, currently superintendent of public schools in Little Rock, Ark., to replace Johnson.