Metrobus, which carries close to a quarter of a million people each workday, gives markedly more reliable service in the suburbs than in the city, a seven-month study by The Washington Post has shown.

Of Metrobus' 10 most reliable routes -- ranked by trips missed or cut short -- eight served the Virginia suburbs and one the Maryland suburbs, operating in predominantly white neighborhoods. Eight of the worst routes ran entirely in the District, primarily in black areas.

The worst routes fanned out from the city core and touched virtually every part of the city, from well-off sections along MacArthur Boulevard to some of the city's poorest blocks near Nannie Helen Burroughs Avenue in far Northeast. Most were punishing runs that kept buses on the street all day and allowed little time for maintenance.

The best routes formed a broad net across Arlington, Alexandria and southern Fairfax, covering Springfield beyond the Beltway, the Pentagon and costly homes near Chain Bridge. Most were rush-hour-only routes, giving the buses plenty of time for maintenance.

The location of the best and worst routes mirrored overall quality patterns, as buses primarily serving Virginia riders completed all but 0.5 percent of their scheduled trips and Maryland's buses all but 1.3 percent. D.C.'s buses missed 2.2 percent of trips. Systemwide, the average was 1.7 percent.

Service quality of the 10 best-rated routes was excellent. They didn't miss a single trip in the survey period; nor did 35 other less busy routes, most of them in Virginia.

Meanwhile, the 10 worst routes missed as many as 7.1 percent of trips, according to The Post's survey.

The study, which was conducted with extensive assistance from Metro workers, examined more than a dozen different types of service and performance records of the more than 370 regular Metrobus routes running between May 1981 and April 1982.

Metro board chairman Jerry A. Moore Jr. and Metro General Manager Richard S. Page acknowledged that D.C. buses fail to run more often, but they said the suburbs are not deliberately favored and that race did not figure in the imbalance.

"There is no racial agenda at Metro," Page said.

Page and Moore said Metro is working hard to correct the disparities. But despite the promises, D.C. bus riders will probably have to live with inferior service for many years to come.

Here are the major reasons:

* D.C. buses get heavier punishment than the suburbs' buses because of the city's transit needs. The typical city bus stays on the road longer each day, logs more miles in stop-and-go traffic and travels on rougher pavement.

* Garage quality is critical to bus maintenance. Suburban garages were newer and better designed than D.C.'s when Metro bought out four private bus systems in 1973 and remain that way nine years later. Though garage renovation work is proceeding, plans to build a new D.C. garage in Southwest are on indefinite hold due to siting problems. Meanwhile, Metro has built a new garage in Montgomery County and plans to spend a majority of its garage-modernization funds in the suburbs.

* Employes' morale and productivity are higher at suburban garages. Due to a seniority system, D.C. garages function as training centers, with the senior mechanics and drivers with superior skills and attendance records moving to the suburban facilities, because working conditions are better there.

Page acknowledges that Metro has been preoccupied with rail construction for years, allowing imbalances it inherited in 1973 to remain. "We've spent too little on the part of our system that costs the most money to operate and carries the most people," he said. Metro is now trying to make up for that.

Service imbalance is only one of a host of problems plaguing the Metrobus system today.

Its 1,800 buses have suffered an epidemic of breakdowns in the last year, caused by long neglect of basic maintenance. Ridership has fallen.

Operating deficits continue to soar, rising to more than $120 million this year. And Fairfax County and Alexandria, which get some of the best service, are laying plans to take over some routes themselves in an effort to escape Metro's hefty costs.

Officials say that modernizing garages can have only limited effect in correcting city-suburb disparities. To a large degree, they argue, unequal breakdown rates are due to area governments' contrasting views of the buses' role in their communities and differing physical environments.

D.C., for instance, has large numbers of low-income residents and a city council that is willing to pay big subsidies.

As a result, the city orders extensive peak and off-peak service from Metrobus, to serve "transit dependent" people headed for work, shopping and social calls.

Consequently, D.C. has a lot of buses like the D8, which ranked seventh worst in the survey and plies an all-day run linking Sibley Hospital and the Veterans Administration Hospital via downtown.

It plods through sluggish traffic, with signals and stop signs every block. Potholes batter the suspension.

D.C.'s rambling Bladensburg Garage has buses that leave the gates at 4:35 a.m. and don't return until 2 a.m. the next morning.

Buses operating three of the routes rated worst in the survey -- the X2, X4 and X6, which run along Benning Road -- have often stayed on the streets 14 hours at a stretch. That means more wear and tear, and less time for oil checks, tuneups and other maintenance.

The city's approach contrasts sharply with the attitude in Northern Virginia, where people are more affluent and less transit-dependent and local governments are less willing to pay subsidies. Service is heavy at rush hour, but light for the rest of the day. As a result, though buses are more reliable in Virginia, it is harder to get around on them because fewer are running.

Buses there tend to leave a garage in the morning for a few hours' duty, then come back for a rest before going back onto the streets in the afternoon. Buses run less punishing routes over better roads. "It's not a continual plying of the streets, stop and go, heavy traffic, clogged streets, like downtown D.C.," says Virginia Metro board member Joseph Alexander.

A case in point is the 17H route, which was rated fourth best in the survey. Its buses run rush-hour only and log much of their mileage on Shirley Highway. Back at the garages, the 17H and other Virginia buses get more time for maintenance, but need less of it.

(Similar factors may help explain an anomaly in the 10-best list, D.C.'s W2. It runs a short-distance, peak hour loop through a Southeast neighborhood. In addition, it is operated by a "midi-bus," one of Metro's smaller vehicles, formerly used on the "Downtowner" routes. These buses are mechanically more reliable than most, Metro says.)

Maryland ranks between Virginia and D.C. in service quality. Routes in parts of Montgomery and Prince George's counties, like Virginia's, have comparatively few stops and starts. But many Maryland buses operated from D.C. garages, which apparently dragged down quality.

D.C. officials believe that a good first step toward relieving imbalances would be a new staffing system. City Transportation Department Director Thomas Downs has proposed ending the current practice of assigning mechanics to garages on the basis of how many buses are there. He would link staffing to how many miles a garage's buses run and how punishing that service is.

This would draw mechanics out of the suburbs. Understandably, it has met opposition there.

There is general agreement in all jurisdictions, however, that D.C. garages are abysmal places to work and must be modernized if they are to attract and keep top-flight mechanics.

"In the dead of winter, you're wearing so many clothes you can't move," says one mechanic at the drafty Northern Garage, a one-time streetcar barn that dates in part to the turn of the century. "You wear long johns, work clothes, coveralls and a coat over that."

Conditions like that bring shoddy workmanship and high absenteeism. For instance, in September, 8 percent of mechanics at Northern, which ran four of the 10 worst routes -- the P1, S3, 92 and C2 -- were absent on workers compensation claims, sick leave and other forms of leave that management feels are abused. At Royal Street, the more modern Alexandria garage, which operates four of the 10 best -- the 11D, 25A, 17H and 25S -- the figure was 4.4 percent.

D.C. garages were far more likely to cancel trips because drivers failed to show up. "It's an extremely dangerous job to work some of these in-town lines," says Charles Boswell, president of the Amalgamated Transit Union local that represents operators and mechanics.

Metro plans to close D.C.'s Southeastern Garage, often ranked as the worst of all, and build a new one in Southwest at a cost of about $17 million. The city's three other garages -- Northern, Western and Bladensburg -- are to stay open but undergo extensive renovation costing about $21 million.

The goal is largely to create more pleasing working environments and foster the good morale found in the Virginia garages.

But it remains unclear how quickly modernization will progress. Much of the program hinges on securing federal funding at a time of cutbacks. In addition, efforts to build the new Southwestern garage in D.C. are on indefinite hold as Metro searches for a site.

"Finding 12 acres of ground in the District of Columbia is almost an impossible task," says transportation chief Downs.

Building in the suburbs tends to move more quickly. Metro's first new garage, the Montgomery County division, opened this fall, and two more garages -- in Landover and Fairfax County -- are planned. That will bring total suburban spending on garages to about $53 million. That compares with the $38 million commmitted to D.C.'s new garage and the renovations.

D.C. officials say they are satisfied with the level of spending devoted to the city and do not feel Metro's plans reflect a bias in favor of the suburbs.

In most cases, quality contrasts are not directly related to type of bus running the route, the survey indicates. The most common bus on the 10 best routes were 1974 models made by AM General, a subsidiary of American Motors. The most common bus on the the 10 worst was also the 1974 AM General.

The exception is Metro's 43 "articulated," accordion-sectioned buses. These high-capacity buses, purchased to save on drivers' wages, are concentrated on the "X" routes and have logged some of the system's worst performance records. Officials blame them for the appearance of three "X" routes among the 10 worst.