When the T-17 bus was late one morning this week on its run from Belair to the Metro subway station in New Carrollton, the director of the Metro bus system hopped into his car and sped down the route to warn a waiting passenger that there would be a delay.

This was hardly usual service from Metrobus, but the passenger and the bus were hardly usual, either.

The passenger was Dick W. Heddinger, a government statistician and a polio victim confined to a wheelchair.

The bus Heddinger was waiting for at Millstream and Moylan Drives in Bowie was equipped with a hydraulic lift that allows a wheelchair-bound person to board the bus. It was late leaving Belair because of mechanical difficulties with the lift on the first bus the driver tried to take out. Metro recently purchased 150 similar buses under a mandate that requires all federally funded projects to be made accessible to the hadicapped.

Metro officials said the law would require them to similarly equip 131 other buses already in service. The cost of hydraulic equipment, repairs and maintenance personnel will total more than $2 million, they said.

The director of special projects at Metro, Hugh Wynn, said Metrobus evenutally plans to equip nearly half its fleet of 1,826 buses with the lifts by 1984.

Heddinger, who normally drives to the New Carrollton station in a specially designed car, was one of the first passengers to use the new bus service. Metrobus began trial runs this week on six routes in Maryland, Virginia and the District. Bus officials hope to begin regularly scheduled, hourly service on 30 routes in June.

The test was conducted with the cooperation of six handicapped volunteers, riding these routes: T-17 in Prince George's county; T-18 in Prince George's and the District of Columbia; the J-2 in Montgomery County; the C-2 in Montgomery and Prince George's; 36 in the District; and 16 serving Arington County, Fairfax City and the District.

When Heddinger's T-17 bus arrived about 20 minutes late, the long-time advocate of public transportation for the handicapped waited for the lift to descend. As the driver pushed the controls, the front steps flattened out and slowly came down to curb level. A flap at the end of the platform flipped down to allow Heddinger to roll onto the platform. He pulled himself onto the platform by grabbing a handrail with his one good arm.

All the while, a buzzer pulsed and a yellow light, decorated with the image of a man with a cane, flashed on the bumper next to the stairs.

Once Heddinger was on, the flap at the end of the platform flipped up to prevent him from rolling off, and the driver pushed his controls to bring the passenger level with the floor of the bus.

Heddinger then wheeled himself to the second set of seats, which were turned up to reveal a seatbelt and a restraining arm which Heddinger pulled to secure his wheelchair.

Once he was settled and the bus drove off, he looked out the window or chatted with his neighbor until he reached the New Carrollton Metro Station. Then Heddinger waited for the passengers to get off. The bus driver prepared the platform for him again. Heddinger alighted, and, after obliging a television crew with a demonstration of the lift and an interview, made his way to the Metro station elevator. He went up to the station platform and waited for an Orange line train to Metro Center. There, he took another elevator and changed to the Red line train to Jucidiary Square. After a trip of about 2 1/2 hours (Tuesday, the run went more smoothly and the trip took 1 1/2 hours) at half-fare price of 70 cents, he began his working day at the Department of Labor.

Of his ride on the bus and subway Monday morning, Heddinger said it was great "getting to work just like anyone else."

Of the delay which made the T-17 and one other bus on the first day run late, transportation officials in other cities where buses have been equipped with lifts, might have said, "we told you so."

The delay, according to driver Johnny Ginn, was caused when the lift on the first bus he tried to take out failed to function. This is a problem that maintenance crews say they have run into frequently in most cities where the lifts have in use.

In St. Louis, for example, breakdowns occur so often that officials of the Bi-State Development Agency, the umbrella transit authority, pour forth a string of complaints when the lifts are mentioned.

"We've spent a half a million dollars on the lifts, and over half of that on repairs," said Andrew Jurchenko, head of maintenance at Bi-State, which has had the lifts since 1977. "The equipment was not engineered, researched or developedenough before it was put to use."

He cited winter weather as the biggest problem, explaining that the ball bearings and other mechanisms under the platform failed to function when exposed to freezing temperature, sand and salt.

Jurchenko said that the transit authority knew the equipment probably would not be successful even before purchase, bu that transit authorities were forced to buy it or lose the 80 percent financing from federal funds.

As for use, Jurchenko said that only about 2 handicapped persons per day use the bus service, but added that if the equipment were more reliable the figure would be much higher.

Asked about the problems with their equipment, a spokesman for Grumman Flxible, which supplies the buses to Metro, responded in much the same frustrated tone used by Jurchenko.

Wayne Aaron, vice president for sales and marketing at Grumman's offices in Delaware, Ohio, said the problem was that the lifts were mandated without consulting the bus industry.

He said his firm was not satisfied with the lift, which Grumman purchases from the Vapor Corporation, but that since it was mandated, "We didn't have a choice. We could put them on the buses or (lose federal funding and) go out of business."

The Vapor Corporation seems to be the only one to take the breakdowns philospohically.

Sales manager William Burrows said that the mechanisms were going through "growing pains" like any new product.

And Metrobus officeals maintain that since St. Louis purchased its first lifts in 1977, some of the mechanical problems had been resolved.

"In St. Louis they started at the wrong time in the fall, they had insufficient experience, improperly designed equipment, and a bad winter. The equipment broke down and people were reluctant to use the buses," said Wynn, at Metro.

Metro has had the new buses on its property for about six months to allow maintenance crews to become familiar with the equipment, make necessary changes in the mechanisms and train drivers. Officals said they hoped the trial runs would allow them the time to make any final changes before offering the service to the general public.

A Council of Government (COG) report said there are about 6,500 people in wheelchairs in the metropolitan Washington area, and about half of them would be potential users of the service.

Advocates of the service, such as Heddinger, estimated that the service would be used by about 6,000 people. Other handicapped people who cannot maneuver stairs will begin using the specially equipped buses as they gain confidence in using public transit, he said.

The lift system on the buses represents the second major victory in six years for advocates of mass transit for the handicapped. In 1973, the advocates saw a $6.5 million authorization signed to equip Metro stations with elevators. CAPTION: Picture, Dick W. Heddinger boards a Metrobus equipped with a lift for wheelchairs. By Joel Richardson-The Washington Post