The treasurer's and sheriff's races in Arlington normally are low-key campaigns overshadowed by the County Board races, traditionally the big draw in local elections. But this year, the campaigns for the two offices promise to be as feisty and hard-fought as the board contest.

The treasurer's race pits two-term County Board Member Dorothy T. Grotos, a Republican, against Democrat Frank O'Leary, an economist with a background in computers, for the job being vacated by Bennie L. Fletcher, a Republican who has held the post for 12 years.

Grotos and O'Leary were among 18 candidates who kicked off their campaigns Tuesday night at the annual candidates' forum sponsored by the Arlington Civic Federation, an umbrella organization for civic groups. Nearly 150 persons attended the session, many of them from the campaign organizations of the candidates and ready with barbed questions for their candidate's opponent.

In the sheriff's race, incumbent Democrat James A. Gondles is being challenged by John E. Baber, a former Arlington policeman who resigned from the force to run as an independent with backing from the Republican and Libertarian parties. Gondles could not attend the forum because he was hospitalized.

Baber turned a question from a Democratic partisan to cheers from his supporters when asked if he had ever lost a police brutality suit against him. He acknowledged an out-of-court agreement, made against his will, in a lawsuit brought by two men he had subdued when he made an off-duty arrest for drunken driving.

With Gondles absent, most of the sharp exchanges were between the treasurer candidates and the four men running for County Board. When challenged on her qualifications for the job, Grotos cited her experience as a member of the County Board, the Northern Virginia Transportation Commission and the Metro board of directors.

"Being treasurer is a management job," she said. "I also believe it is a public relations job. You are dealing with all the citizens of Arlington . . . the citizens deserve someone who has a record. And I think I've shown I'm dedicated to Arlington County and care about our citizens."

O'Leary, criticizing 44 years of Republican control of the treasurer's office, said that "the taxpayers cannot afford to lose tax revenue through apathy, indifference and poor money management." He said that Arlington has "by far the highest tax delinquency rate" in Northern Virginia and criticized the treasurer's methods of investing public money.

In the County Board race, Democrats Richard A. Buffum and Albert C. Eisenberg sparred with Republicans Walter L. Frankland, who is seeking his third board term, and former school board member Michael E. Brunner.

In a discussion ranging from the importance of maintaining neighborhood services in developing areas to housing and transportation issues, the two Republicans stressed the need for political balance on the five-member county board, now controlled by three Democrats.

Buffum and Eisenberg countered that citizens deserve, as Eisenberg said, "a distinction between mere tenure and service."