Incumbent Republican John J. Buckley and Cambridge Mayor Walter J. Sullivan were locked in a close battle for the post of Middlesex County Sheriff at press time this morning.

Fragmentary returns, as of 3:30 a.m., gave Buckley 87,237 votes to Sullivan's 64,979 out of an estimated 500,000 votes cast in the county, which includes all of Cambridge as well as Boston's northern and western suburbs.

Democrat Sullivan was the favorite in the race because of his strong organizational base in Cambridge and the expected statewide Democratic victory.

With all but two precincts reporting, Sullivan led in Cambridge by just over 1000 votes, 14,579 to 13,399.

Sullivan predicted last night he would win by 15,000 votes, counting on his strength in Cambridge, Lowell and Somerville.

Buckley's campaign manager said early this morning that the Sheriff was leading by 5000 votes out of 125,000, according to his own totals.

Buckley predicted that the contest would go "right down to the wire." He said he was "fighting a country-wide Democratic sweep."

In the Cambridge 4th Middlesex district, which includes Inman Square and Riverside, 30-year Democratic incumbent State Rep. John J. Toomey easily defeated Grass Roots Organization candidate City Councilor Saundra Graham. With all but three precincts reporting, Toomey led Graham 3206 to 2630.

Incumbent State Rep. Thomas H.D. Mahoney, a MIT professor, trounced his Rupublican challenger Edwin B. Newman, professor of Psychology, in the second district, located in the Brattle Square area. With three-fourths of the vote in, Mahoney led, 3235 to 2136.

Buckley called the gun lobby a "very, very powerful" factor in the election. Buckley favors a ban on private possession of handguns.

"Issues made the race exciting," Buckley said. "If I win, my progressive stands on prison reform, gun control and the legalization of marijuana will catch on," he said.

Sullivan said last night that his administration would be marked by "good administration, hard work and good organization."

Buckley, who said he considers himself "an agent of social change," said he has made no plans in the event of defeat. A Guggenheim Fellow at the Yale Law School, Buckley said he would begin lecturing there early next year