Maryland officials who oversee the state's 16-month-old auto emissions testing program say they are working the bugs out of a process that, in general, they describe as a success because most cars are passing inspections and air quality in the Baltimore-Washington corridor is beginning to improve.

Some car owners have complained to state officials, however, that unreliable test results -- and the return trips that are required -- make the process a real headache.

Despite that, "We're having only one fourth as many complaints as we had before," when the program began, said Bruce Diehl, the state Motor Vehicle Administration's manager for emissions inspection.

Initially, Diehl said, some people had difficulty getting their vehicles to pass inspection, either because of improper maintenance of the emissions systems or because of the design of their vehicles. At the beginning of the program, about 80 percent of the vehicles passed inspection. Now, Diehl said, about 87 percent of vehicles pass on first testing.

In recent months, some of the rules have been changed to make allowance for the kinds of vehicle that produce vastly different readings, he said.

For example, some Fords and Hondas are designed to conserve power by automatically shutting off a valve in the catalytic converter when the car idles too long, he said. Diehl said test operators now know to have drivers turn off those engines while waiting in line at testing stations and restart them again before the test is made.

In 1984 the state began requiring car owners in the Baltimore-Washington corridor to have their vehicles' exhausts tested for excessive pollutants. The test, available at 10 state stations, costs $9. Drivers whose cars fail are not charged for one retest, but a third test costs $5.

The 10 stations -- in Prince George's, Montgomery, Anne Arundel, Howard and Baltimore counties and Baltimore City -- are run by a contractor, Systems Control Inc. of California, a subsidiary of British Petroleum. The centers test about 1.7 million vehicles a year, Diehl said.

The program is administered by the MVA and monitored by the Department of Health and Mental Hygiene, which checks the meters each month for accuracy of the readings.

James Clark, a Montgomery County resident, said he has taken his 1979 Honda Accord in for testing three times since March, all at the Briggs Chaney Road station, but still has not passed the emissions test.

After the first inspection, Clark said, the operator told him the Honda had passed. But Clark said the computer printout he was given, showed that his car had flunked. When he pointed it out, a mechanic at the testing station told him he needed new spark plugs and a distributor cap.

After those repairs were completed, Clark said, he took the car back to the testing station, but the hydrocarbon reading was still too high. He returned a month later to try again, and flunked again. Clark is now trying to get a one-year waiver on the inspection, allowed for owners who spend more than $50 on state-directed repairs to upgrade car exhaust.

Vincent Wong, an automotive specialist for the American Automobile Association, said he had a similar problem. He took his 1980 Oldsmobile Cutlass to the Briggs Chaney Road station in January, but the analyzing machine apparently was not working correctly.

"The operator kicked the machine . . .then he told me I failed," Wong said. "I looked at the reading and I knew there was no way my car had failed." A short time later, Wong said, he drove to the western Montgomery station near Gaithersburg, "paid for another test and breezed through."

Wong said he believes much of the problem can be attributed to the fact that "the operators are not certified mechanics. They have no idea what they're reading."

According to Diehl, the contractors use operators who have had about 28 hours of training.

"I think we're operating a top-notch program here," said Thomas Snyder of the air management division of the state health department. He said that while there are still some problems, the inspection failure rate continues to drop.

Snyder said that earlier this year, he began having the analyzer machines audited every month instead of once a year, as required by the U.S. Environmental Protection Agency. In 1984, Snyder said, his staff found only five defective machines out of about 50.

Snyder also believes another reason behind the declining failure rate is the fact that "people are getting the idea of repairing their cars on a timely basis."

In the meantime, air quality in the Baltimore-Washington corridor appears to be improving, said George Ferreri, director of Air Management for the state. Carbon monoxide levels seeem to be dropping, Ferreri said. And, based on the fact that more cars are passing the inspections, his staff believes that the hydrocarbon level in the air is also going down, he said, although tests are inclusive now.

But the jury will be out on Maryland's emissions program until the legislature decides in 1988 whether the program should be continued. A Government Accounting Office report published last January was critical of similar emissions inspection programs in 30 other states. Maryland was not part of the study.

The report said the benefits of such programs were often inconclusive because many of the programs were not well-managed and their quality control was questionable.