Some Northern Virginia financial officials were uncertain yesterday exactly how a measure pending before Congress that would exempt out-of-state representatives living in Virginia from paying personal property taxes would affect local revenues, and one questioned its constitutionality.

The House District appropriations subcommittee yesterday approved the measure, which would bar states from imposing the tax on a car used by a member of Congress for going to or from work unless the member represented the state in which it was being driven.

Because Virginia is the only local jurisdiction to impose personal property taxes -- on cars, boats and planes -- those members of Congress living in Maryland and the District of Columbia would not be affected. Virginia members, who pay the taxes, would continue to do so.

"It wouldn't have a significant financial impact on us," said Jean Marshall Crawford, Arlington's deputy commissioner of revenue. "But there's a fairness issue involved and questions about Congress' jurisdiction over local governments."

Crawford contends that Congress doesn't have such jurisdiction, and has asked the Virginia attorney general's office for an opinion on the issue. While the U.S. Constitution guarantees members of Congress exemptions from certain criminal prosecutions, she said, it says nothing about their ability to exempt each other from locally imposed taxes.

Paul Henneberry, Alexandria's assistant director of finance, said he had no estimate of what the financial impact of the legislation would be, but doubted it would be significant. Fairfax County officials could not be reached for comment yesterday.