John E. Baber, who quit the Arlington police force last month to run for sheriff, won the Arlington Republican Party's endosement of his independent candidacy last night..

Baber outpolled Charles Bonneville, 813 to 672, in what party officials said was the largest turnout for a local GOP runoff ever. The runoff was required because none of the three candidates seeking the party's endorsement at last week's Republican canvass won a majority. A third candidate for the endorsement, David Ryan, was eliminated last week.

Baber will face Democratic Sheriff James A. Gondles in the fall. As an independent, rather than the party's nominee, Baber hopes to win the support of Arlington residents who are federal employes barred by the Hatch Act from active participation in party politics.

Baber collided with Arlington's own version of the Hatch Act this year. A patrolman on the police force for more than 14 years, he was told county law required him to resign or be fired if he ran for public office. He filed suit to overturn the law, lost and is now appealing. He resigned from the department last month to run.

On Saturday, the County Board voted to liberalize its "mini Hatch Act" so county employes who are not Arlington residents can run for office elsewhere. Under the new rules, a county employe may participate in statewide political campaigns, such as the governor's race. But they are still barred from running for or participating in county races and those for state offices based in Arlington, such as the sheriff's race.

The sheriff runs the county jail and performs a variety of other functions, including serving court papers such as summonses and subpoenas.