On a breezy, fall evening at the Rhode Island Avenue Metrorail station, Maryland-bound passengers are casually climbing aboard the bus to Capital Plaza. Slowly, the seats fill with school children and adults on their way home from work.

Sitting at the wheel is a rail-thin, middle-aged Metro driver. Every now and then someone sticks his head in the door and attempts to ask a question: "Does this bus go to . . .?"

"Captial Plaza. I'm not going any farther than Capital Plaza," the driver barks.

A few minutes later, the driver closes the doors and turns face his passengers.

"Could someone hlep me?" the driver asks, with a tone of bewilderment. "I'm going to Capital Plaza. I've never been to Capital Plaza, and I don't know how to get there. Does anyone know the way?"

Silence suddenly engulfs the bus. The driver scans the faces of his passengers, searching for help, while passengers look at each other in amazement. Finally, a voice pipes up from the back of the bus.

"Yeah, go on, man. We'll help you," shouts bearded young man. Then, turning to the man next to him, he whispers, "Ain't this a b . . .?" The bus driver doesn't know where he's going!"

The bus rolls out onto Rhode Island Avenue.

"Do I stop for passengers along the way?" asks the driver.

"Only as they flag you down," responds another passenger.

Conversation that had been about personal matters now turns to lively chatter about the bus ride. Every now and then a new passenger boards the bus and hesitates as he hears a passenger call out directions and watches the driver submissively obey. A hijecking? No, he is reassured, the bus driver is just lost.

The 20-minute ride is unevenful, except for one noisy but friendly conference between passengers about where to turn. But they work it out as the driver waits patiently for their decision.

Finally, Capital Plaza is within sight. The few remaining passengers relax.

"An . . . how do I get in here?" the driver asks.

A passenger directs him into the final stop. They all descend from the bus chuckling softly. But a thought comes to one passenger.

"Do you know how to get back?"

"Yeah, I'm all right now," he says. "Thanks. I can find my way back." In a moment he is gone. Off to somewhere in Maryland.

How often do Metro bus drivers get lost? More often, apparently, than Metro would care to admit. More often that drivers like. But, according to drivers in the Bladensburg division, it does happen.

It usually occurs, they say, when a driver has been placed on an extra service route with which he is unfamiliar. Extra-service buses are scheduled when there has been a bus breakdownj, an unexpected shortage of drivers or sudden rescheduling of Metrorail lines. For example, on Oct. 3, 43 extra service buses were run between 11:40 a.m. and 8:30 p.m. because of a metrorail power failure at the Eastern Market station.

"No driver likes to give the impression he doesn't know what he's doing or where he's going, but sometimes you have no choice," said one veteran driver who has asked passengers for assistance when on unfamiliar ground.

"Most of the time people are anxious to get home and they're only too willing to help the driver."

Another driver, reluctant to appear uninformed and embarrassed to ask for directions, said he has devised a different method.

"Me, I won't get myself in that situation (of having to ask for help)," he said. "I use my own kind of way to get there. I might miss a street or two but I know where the lines cross and I get there.

Metro officials contend that extra service buses are rarely needed. And while some drivers may not have driven a route for a long time, they add, a driver is never lost.

Most of the drivers who take extra service assignments when necessary are what are known as "board men," explained Metro official Thomas Trimmer. These drivers are assigned different routes daily, which are posted on a bulletin board a day in advance. Drivers on the board are required to be familiar with the city routes in their division and Trimmer insists that they are.

This can be a sizable task. There are 110 routes and 38 lines in the Bladensbrug Division alone, he said. In addition, he said, each driver has a route book to which he can refer.

"You can't remember everything out of the book," said Johnny Adams, a driver with four years of Metro experience. "No driver knows every run. That's why they have a bulletin board to let you know what you have to do ahead of time. "(And) there's no sense in asking the supervisor directions when you can ask the passengers. Some are glad to help, and others are a little reluctant."

"No driver knows all the runs," said Theodore White, a Metro supervisor and 10 year company veteran. Realizing this, White said he never sends a driver from one division onto an unfamiliar route in another division unless be's forced to. When this happens he asks a passenger to assist the driver.

"I don't know what any other supervisor does but that's what I do," said White. "I'll walk up to the waiting passengers and say, is anybody here going all the way out (to the end of the line)? We have a small-problem here. The operator is unfamiliar with the someone always complies," said White.

"When you do extra-service you have to do what the man tells you," said Johnny D. Whitaker, a Metro driver for five years who says he has never been lost. "I know all the routes in the Maryland division, in the District and half in Virginia," about 300 runs in all.

Whitaker quickly dispelled the idea that some drivers devise their own routes. The passengers wouldn't allow it, he said.

"If you ride a bus every day you're not going to let that driver make a wrong turn.

The only way a man would get away with that is if he's been on a run a long time, he knows the passengers and they just won't tell on him." These drivers don't devise their own routes, said Whitaker, they just take short cuts.

"If you're on a run every day you've taken all kinds of short cuts to get off early.I know that's been done," he said.