The Arlington County treasurer's office filed a $25,000 suit yesterday in Circuit Court against a former chief deputy sheriff, alleging that he illegally purchased a truck at a sheriff's auction in 1985.

County Treasurer Francis O'Leary Jr. alleged that Ronald Hager, who resigned from his post earlier this year to run for sheriff against incumbent James Gondles, violated state and county laws that bar public officials from directly or indirectly bidding on or purchasing property sold at such auctions or using their positions for personal gain.

"He has retained the truck illegally and we want it returned to the county," Kevin Appel, attorney for the Arlington County treasurer's office, said yesterday.

Appel said the county is suing for $25,000 in damages and wants the truck returned so it can sell it and recoup $189.95 in taxes owed by a previous owner. The assessed value of the truck, which Hager purchased from a Springfield man for $25, is $1,312.

"I haven't been informed of this suit," Hager said yesterday. "I have not done anything illegal. This is just an attempt to embarrass me. This charge is politically motivated."

The suit comes in the midst of a bitter campaign battle between Gondles, a Democrat, and Hager, a Republican-backed independent.

"O'Leary is on Gondles' campaign staff," Hager said yesterday. In an interview last week, O'Leary said, "If my actions were politically motivated, I would have waited until a month before the election to make these charges."

According to Appel, the 1979 Datsun truck was initially seized by the county after its owner failed to pay personal property tax, penalty and interest on it. In February 1985, the truck was sold to Daniel Saenz for $25 at a sheriff's auction. Saenz transferred the title to Hager a few days later, after Saenz paid the titling fees, Appel said.

Hager said he approached Saenz, whom he said he did not know, after the auction and asked him if he could buy the truck.

Appel said he could have asked the sheriff's office to confiscate the truck from Hager but declined, saying he was confident Hager would not leave the area with the truck.

Because there are few precedents in Virginia of public officials charged with violating this law, Appel said he looked at similar cases in other states to see how they were handled to prepare the suit filed yesterday. Commonwealth Attorney Helen Fahey said she has consulted the state attorney general to determine whether this kind of violation is criminal.

"The statute says you shall not do this but it doesn't say what will happen to you if you do," Fahey said, adding that she expects to hear from the attorney general next week.