Northern Virginia motorists will not escape from a new state law mandating annual exhaust tests for most cars in the region.

Gov. John N. Dalton, citing the potential loss of $37 million a year in federal highway funds, today vetoed legislation that would have suspended the tests, which began earlier this month.

Dalton said that while he sympathized with motorists opposed to the new federally mandated tests, he had been warned by high-ranking Environmental Protection Agency officials that the Virginia suburbs could lose all highway construction funds and that new industrial development there could be curtailed under federal law. He also cited "the economic hardship to the inspection stations wherein expensive equipment has already been purchased to conduct these inspections."

Del. David Brickley (D-Prince William), who sponsored the emergency legislation passed last week, called the veto "a real kick in the pants to Northern Virginians." Brickley charged Dalton had acted not out of fear of federal sanctions but because of intense lobbying by car dealers who fear losing money on their investment in test equipment.

To date 135 private garages in Northern Virginia have begun the inspections, which are required annually. Maryland and the District of Columbia, which are planning centralized state-run inspections, are not scheduled to begin them until January 1983.