Parnell Roberts, a 65-year-old man who wears baggy old clothes, often waits just inside the doorway of the Trailways bus station in downtown Washington. But he isn't going anyplace. Unlike the thousands of travelers who pass him by each day without a glance, Roberts is a man without dreams or destination.

Roberts was a traveler once - some 30 years ago - when he came to Washington with hopes of making it in construction work. Somewhere along the way his dreams dissolved and he now has time to linger at one of Washington's two bus depots.

Robert's sad, bloodshot eyes drift off into a blank stare during the long, silent moments between his sentences. The words come slowly. He says he lives off a $179 a month Social Security check but does not have a place to stay. He chose the bus station "to be around people."

There are always people at the two downtown bus terminals, the Trailways terminal on 12th Street, and the Greyhound Station across New York Avenue.

There are the old drunks, the pimps, the hustles, the pick-pockets and the down-and-outers. There are also the travelers, young and old, black and white, who wait for the groaning buses which belch exhaust as they come and go.

The bus rider is part of the unglamorous side of American travel. In Washington, he is most probably black and earns less than $8,000 a year, studies show. According to Trailways officials, 43,000 travelers bought tickets in the last three months at the Trailways terminal in Washington. They were part of the 340 million passengers who ride buses annually nationwide.

At Greyhound, Larry Kratzer, who is in charge of operations, said 350 buses - on the average - arrive and depart from the terminal each day. He could not give figures for the number of passengers who ride Greyhound.

Meanwhile, Ted Knappen, senior vice president of Trailways, said his company spent $750,000 in 1976 to renovate the downtown station and install a Hardees Restaurant.

Greyhound spent more than $1 million that same year to modernize its facility and add a Burger King Restaurant, a spokesman said.

The two bus stations with their pay toilets, fast food restaurants, trinket shops and plastic-seat waiting areas are stages where tragedy and drama are often played out and where adventure is often launched.

Adventure was in the eyes of 27-year-old Marilyn Johnson of Los Angeles, who recently arrived by bus from West Virginia, where she had visited her boyfriend. She sat alone in the Greyhound bus station at 10:45 p.m. waiting for a bus to New York.

"I decided to take the bus to see America, but I'm always traveling at night," lamented the tall, lanky brunette, who constantly pulled her stringy hair back from her eyes.

Johnson said she planned to take the bus from Washington to New York and then to Canada. From there she would ride a train to Seattle where she would again climb aboard a bus bound for Los Angeles. "I'll do it if I don't chicken out," she said.

The adventuresome traveler, who complained of being accosted by strangers on the streets of Washington near the bus station and sleeping in a "sleazy hotel," said she was taking a late bus to New York to save $11.

"I will arrive in New York at 4 a.m. and I will probably have to stay awake until the sun comes up before I find a safe place to sleep," added Johnson.

A few minutes after Johnson boarded her bus, a small drama unfolded. It began in front of the Greyhound terminal and involved a domestic quarrel between a couple in their 20s.

It was midnight. Their screams awakened an elderly woman who had been sleeping against the terminal's wall, cuddling a brown paper sack filled with clothes.

The argument spilled into the bus station and out again, and the young woman was slapped several times by the angry man. He yanked her pocket-book away. She yanked it back.

Both the man and woman claimed the other was drunk and swore not to return home.

Only moments later inside the Trailways bus station, a woman screamed and a security guard chased a pick-pocket out of the terminal.

Across the street from Greyhound, a grey-haired wino, wearing an old blue "Jaws" T-shirt and a tattered overcoat, was sleeping. Earlier that day, a security guard had wrestled him out of that station and drained the man's bottle of liquor on the sidewalk.

Not every person hanging around the bus station is a wino or vagrant.

It was 2:30 a.m. when 44-year-old Samuel Mitchell began philosophically discussing why "winos" and others spend their time sleeping in bus stations when they could sleep in District-run shelters - or, in some cases, their own "nice homes."

"I don't know what's wrong with those people. .fs. wait a minute. I don't know what's wrong with me. I'm a mechanical engineer, I make good money, but I'm here at 2:30 in the morning spending my time talking to you."

Mitchell said he has felt lonely since his recent divorce so he either lingers at the bus terminal, Ben's Chili Bowl, or the pool hall.

"I know everybody who works at the bus station on every shift - and every bum," he beamed.

"You see a little bit of everyting - anywhere from bums, winos, pick-pockets to vagrants," said 34-year-old D.C. policeman Allen Fant, who has walked the District 1 police beat near the bus station for the past eight years.

Fant, who was in the middle of an argument with a taxi driver he had ticketed for refusing to pick up a passenger, agreed that many vagrants do not take free meals or sleep in the shelters provided by the city. "They prefer to stay at the bus stations whether it is hot or cold," he said.

"The pimps stay here waiting for the runaways. They know the young girls are vulnerable. The pimps let them know they have a place to stay and it is later when the girls find out they have to work to earn their keep," Fant said.

One of the security guards who has worked in both the Greyhound and Trailways bus staions says that he has to constantly patrol the bathrooms to control homosexuals.

"It's really bad down there. There are guys in there just looking for trouble," said security guard Herman L. Boddie.

One of the problems at the bus terminals, according to security guard Russell Tolson Jr., is that the "courts just put the bums back on the street." He says it's like a revolving door when the security guards throw the vagrants out of the terminals.

"We throw them out of one terminal and they go to the other," Tolson complained.

A spokesman for District 1 police headquarters said that despite the complaints by security guards, crime in general has gone down in the last five years in both bus terminals.

Officer Thelma Arlington, who compiles crime statistics for District 1, said most of the crimes in the bus terminals are minor offenses such as pickpocketing and loitering.

For more than 25 years, 46-year-old Charles Gamble, a baggage handler at the Trailways station, has watched the crowds flow in and out. He said life has gotten better at the station over the years.

Gamble, who is slim, black and still wears the "red cap from the old days," said Trailways officials gave jobs to black drivers back in the early 1970s when the predominantly white group of bus drivers went out on strike. When those bus drivers returned, he said, the black bus drivers kept their jobs.

There have been more opportunities for blacks recently, according to Gamble. He said the company has implemented a policy to train new people so they can be promoted . . . "so they will not be left behind like I was . . ."

According to Gamble, new Trailways employes are given training in a number of areas so they can be promoted into any job.

Gambles' counterpart at the Greyhound station is Roy Brown. He is a maintenance man who said he has worked at the terminal for 28 years.

As Brown talked, he pushed a broom under the plastic seats in the waiting area forcing sleeping travelers to raise their legs so he could sweep. He said before the modernization in 1976, the terminal was "really messed up."

Meanwhile, Briggett Gondelock, who wore a three-piece violet suit, sat patiently waiting for the bus to Seattle. "I've just dropped out of school and now I plan to get in some tennis; go down to L.A., and find a job."