When you take your car to a District of Columbia inspection station, its exhaust system will now be checked for compliance with federal and regional air pollution standards.

Thomas Downs, the city's transportation director, was joined by Jerry A. Moore Jr. (R-At Large), chairman of the City Council Transportation and Environmental Affairs Committee, at the start of the program yesterday at the Southwest inspection station, 1001 Half St. SW.

All cars will be checked with electronic devices at both municipal inspection stations. They will be given arithmetical ratings along with either a "pass" or "fail" grade for two types of pollutants, smog-causing hydrocarbons (from unburned gasoline) and carbon monoxide (gas from incomplete combustion of gasoline). The devices also will monitor each car's fuel efficiency.

Eight of the measuring devices, which include probes inserted into exhaust pipes, were bought for $14,000 each with grants from the Environmental Protection Agency, Downs said.

For now, car owners need not do anything about a failing grade, although Downs said it would be to the community's and their own benefit to do so. But starting next Jan. 3, owners of flunking cars will be denied inspection stickers until adjustments or repairs are made. Downs said these may be done at private automobile repair facilities that will be designated throughout the city.

Downs estimated that only about 20 percent of the inspected cars will flunk the test. But, he added, those cars cause half of all vehicle-triggered pollution.

The new tests will be financed through a $2 increase in the annual car inspection fee, now $3, which is paid by car owners when they obtain their license tags. The increase was approved recently by the City Council.

Exhaust tests are required for this and other major metropolitan areas under federal clean-air rules. On the Eastern Seaboard, they already are being conducted in Northern Virginia as well as in New Jersey, the New York metropolitan area and Rhode Island. Maryland plans to start its program next year.