The old silver bus with South Carolina license plates reached the 14th Street bridge approach into the city about 10:30 last Wednesday night. Inside, in the darkness of the coach, a thrill ran through the passengers--29 seniors and three faculty members from a small high school in the foothills of Hogback Mountain who had been riding since dawn on a 500-mile journey that was, for most, their first trip to Washington.

Now the Washington Monument loomed, all lit up in the night, more impressive even than it had looked on TV and in books. And one after another more landmarks came into view, luminous and grand. Sarah Glenn, an English teacher since 1946, who leads the seniors of Blue Ridge High School to Washington each year with as much enthusiasm as if it were her first time, could hardly keep up: "There's the Jefferson Memorial . . . and the Capitol . . . and the Kennedy Center . . . Lincoln Memorial . . . . "

They all stared out the windows, some silently but most chattering in awed voices. "Oh, Doris, it's gorgeous!" Veronica Byrd, the class track star and gospel singer, said to a friend. The students wondered aloud about the height of the Washington Monument, the identity of the bronze figure atop the Capitol, the function of the Kennedy Center.

But there was little time to consider the marble grandeur of the city's historic buildings. Minutes after the bus passed the Capitol, it reached downtown 14th Street, with its strip of neon-lit adult movie theaters and porn shops advertising sights of another kind: "Samantha Fox in 'Blue Ecstasy' " at the Casino Royal; "Nudes, Nudes, Nudes" at Benny's--Home of the Porno Stars; " 'Doc' Johnson Marital Aids" at Paradise Adult Books; "The Sexiest Dancers--Topless, Bottomless" at The Butterfly. And there in the middle of it all, incongruously, was a U.S. Post Office, right between Gold Rush ("Fantasies Unlimited") and the Adam and Eve Book Store ("Exotic Books and Magazines").

The first people the students from Blue Ridge saw in Washington were greasy-looking men hawking the enticements of exotic nude dancers, high-heeled, heavily made-up women who looked like prostitutes, ragged panhandlers, gawking tourists. The students gawked, too; they had never seen anything like this in Greer ("Heart of the Piedmont"), the town closest to their homes.

The driver of the bus, a soft-spoken white-haired man from Spartanburg, S.C., named J.C. Kimbrell, looked around with some measure of alarm. A man lay on his back in the brightly lit doorway of Bostonian Shoes. Kimbrell spoke in a voice much louder than usual: "I don't want anybody to look at these people." So of course everyone looked even harder; it was fascinating and also, most of the students agreed afterward, "disgusting." But it was on 14th Street, of all places, that they spotted their first familiar beacon: McDonald's. Mrs. Glenn laughed. "Now, do you feel at home?"

Donna Emery, captain of the color guard and editor of the school newspaper, said disapprovingly, "It's weird that President Reagan drives up and down this street and doesn't do anything about it." The bus approached Thomas Circle. A statuesque woman wearing a tight black velvet jacket, stockings, high heels and, apparently, nothing else, walked coolly along the sidewalk, unaware that 29 high school seniors from the South Carolina hills were staring at her and would talk about her for days afterward ("She wasn't wearing any pants!"), as they would talk about many of the strange-looking people they viewed on the streets of Washington.

It had cost them $150 apiece, not including food, to come to the city for three nights and two days. They stayed three and four to a room in the Sheraton Washington Hotel, expensive and unnecessarily luxurious, Mrs. Glenn said, but the only hotel where they could find rooms when they began checking last December. They were 32 among thousands of tourists--between 75,000 and100,000, according to the Washington Convention and Visitors Association--who visited the city during a week that was busy for those in power. The secretary of state was attempting to mediate the Falkland Islands crisis. The Senate Foreign Relations Committee opened hearings on an $8.7 billion foreign aid package. The president flew to Chicago to give a speech and flew back the same day.

None of this held much interest for the 29 seniors from the school near Hogback Mountain. They were busy seeing the sights on a nonstop schedule set by Mrs. Glenn, a onetime high school softball and basketball star, who walked faster than anyone in the group and challenged: "The first requirement is to keep up with me. When I have two days to see Washington, I'm going to see Washington. I'm not going to waste time eating or going to the bathroom."

She didn't waste a minute.

The first night, last Wednesday, the group went straight to the hotel. That left two days and two nights. In that time, Mrs. Glenn led them, in this order, to: The Bureau of Engraving and Printing, Federal Reserve, Washington Cathedral, Museum of American History, Museum of Natural History (twice), Arlington Cemetery, Air and Space Museum (twice), National Zoo, Library of Congress, Supreme Court, the Capitol (including a picture-taking session on the steps with their senator, Strom Thurmond), National Archives, Lincoln Memorial, Jefferson Memorial, Washington Monument. They would have done more, but time was lost standing in lines (one hour at the Monument) and stuck in traffic. They went everywhere in the ungainly 39-passenger vintage-1953 silver bus known as The Baby Elephant, which didn't always find the quickest way. Mrs. Glenn never faltered. "If I weaken, they'll never know it." None of the students saw her take two aspirin at dinner Thursday night; her neck was hurting, the result of a serious whiplash she had suffered in a car accident.

The closest they got to the White House was seeing it from the bus as they went down Pennsylvania Avenue. "There's the White House," Mrs. Glenn said each time they passed, and the girls would sigh with longing to see the Red Room, the Green Room and the Blue Room. They tried, through their congressmen, to get inside, but they were told they would have to wait with all the other tourists in the public line, and it was too long for a group with only two days in Washington.

The seniors from Blue Ridge showed no interest in the Watergate. "They were in the second grade during Watergate," said guidance counselor Doris Dobson, who also accompanied the group. Nor did they visit the city's most fashionable neighborhood, Georgetown. They had never heard of it. Theirs was a budget Washington. The only shopping they did was at souvenir stands. They ate no great meals, though they did have a few memorable ones, most notably at the McDonald's on 14th Street, where they sat next to three women they were sure were prostitutes, and the Sholl's Cafeteria at Vermont and K, where they felt sorry for the bag ladies and bums whom everyone else ignored.

They were enthralled by the Air and Space Museum and the view from the top of the Washington Monument. They were deeply moved by the Washington Cathedral and Arlington Cemetery. Most were understandably worn out and bored by the time they hit the National Archives Friday afternoon. They were unfailingly polite to the people they met--tour guides, guards, waitresses, souvenir salesmen. Not everyone returned their courtesy. They were frequently urged to move more quickly--by a guard at the Capitol, who barked at them to hurry through the revolving doors (the doors held special interest since no one knew of any revolving doors in Greer), by the women behind the cafeteria line at Sholl's, by the guard supervising the endless line at the Washington Monument.

The students from Blue Ridge High said they had a wonderful time in the Nation's Capital, but most agreed with Roger Fowler, a congenial young man who wants to grow peaches, like his father: "It's a whole lot different up here. It's too fast. And the buildings are packed so close together. I couldn't live here."

And with Tracy Jeffeaux, who marches in the award-winning school band, hopes to become a radiologist and said, with unintentional understatement: "People up here think success is making $50,000 a year and having a $55,000 house. It's not. Success is happiness."

Tracy and Roger and the 27 classmates who came to Washington belong to a graduating class of 120, the largest in the history of Blue Ridge High School, which has 620 students and 32 teachers, grades eight through 12. It also was the smallest group that had made the Washington trip. "Hard times and economics," said assistant principal Tom Sizemore, one of the three chaperones. There are 80 black students, most of whom travel to school on one bus, from the town of Taylors. Seven of the teachers graduated from Blue Ridge. The principal was in the Class of '68, and he, like other Blue Ridge students, drove one of the school buses, for $45 a month. Many of the students have parents who also went to Blue Ridge. Thirty percent of the seniors go to college, but they don't go far. They attend Clemson and Furman universities, Greenville Technical School, North Greenville Junior College. No one this year plans to attend an out-of-state school.

On the wall above the clock in the school cafeteria is a prayer composed by a Blue Ridge graduate: "We pray that Thy love upon this food be shed. And while at school, dear Lord, may our minds be fed." The students go to church faithfully. In the dogwood, pine and poplar-shaded hills surrounding the school are 40 churches and a beautiful view of the Blue Ridge Mountains. The closest town is Greer, 10 miles away. Greenville ("Textile Capital of the World") is the closest big city. Most of the parents of the Blue Ridge students commute to blue-collar jobs in Greer, Greenville and Spartanburg. Many work at J.P. Stevens, Celanese Plastics, Southern Machinery. Some, like Roger Fowler's father, are peach farmers. By this time of year at Blue Ridge High, many of the senior girls are wearing small diamond engagement rings. Among those who came to Washington was Gloria Ball, who on June 5 will marry a machinist named Richard Brashear and move into a trailer on Rte. 1--"almost in my mother's front yard," says Gloria.

Graduation from Blue Ridge High is "a solemn occasion, like a church service," says Principal Kenneth Southerlin. "A lot of their parents didn't graduate from high school, and they take a lot of pride when their children do." After graduation most will stay close to their friends and families, and to the mountains. They like it where they live. Mr. Southerlin, 32, who was born and raised near the school, didn't see Washington until a few years ago, when he accompanied the seniors on their tour of the memorials and government buildings. "You see what you've studied all these years," he said. "There's nothing like seeing Washington for the first time. It's different from what you expect. It's more overwhelming. No one can describe it. You can't read about it. You've got to go and see it."

And so at 5:45 a.m. last Wednesday the 29 seniors, their parents, their boyfriends and girlfriends, and their three chaperones gathered in the parking lot at Blue Ridge. The sun had already risen; you could see the top of Hogback Mountain. Just before the bus left, Veronica Byrd's mother stood next to the driver and said a prayer: "Lord, thank you for giving these children this privilege . . . . Help them to enjoy this trip and remember it for the rest of their lives." Veronica cried.

The bus headed down the hill to Rte. 29 and then on I-85, bound for a city that was, to most of the 29 seniors from Blue Ridge, "a vague place, like something out of the movies," according to Mr. Sizemore, the assistant principal. He laughingly remembered his own far less exotic senior trip, with the Greenville High School Class of 1954. "We got on the school bus and visited six plants. Everyone stood around and said, 'This is great.' " To the students, Washington was a historic city filled with important people. It also was a dangerous city. The president had been shot there. Mrs. Glenn had warned: "Watch your hip pocket, don't ride elevators alone, don't talk to strangers and don't buy flowers." One year in Washington, she said, the Moonies were everywhere, selling flowers.

Allen Cox, centerfielder on the champion Blue Ridge baseball team, sat beside his girlfriend, Candace Lynn, cheerleader and homecoming queen. He wondered, "Are there gang wars in Washington?" There are no gang wars where he lives. The closest thing to a gang is the group of boys--Allen Cox and his friends Roger Fowler and Johnny Farmer and David Barnette--who like to go to Jimmy Tooley's house on weekends to play basketball and sit around and talk. The only vandalism incident anyone can remember at the school occurred a few weeks ago when one student had the tires of his car slashed in the parking lot. Drugs are not a problem at Blue Ridge. "I suspend fewer than a dozen students for drugs each year," Mr. Southerlin said. "By drugs I mean marijuana."

The old silver bus that brought the Blue Ridge seniors to Washington is owned by the gregarious Mickey Ward, who used to be the bandleader at Greenville High. He couldn't do the driving this year because he had to get ready for the World's Fair in Knoxville; he needed to buy a second and third bus. Ward, 44, felt bad about missing the trip. "I'm always sorry when I can't be with that bunch of kids . . . . I love Washington. It's always spine tingling when you reach the crest of that hill in Alexandria and see the Pentagon and the city, all laid out before you."

J.C. Kimbrell, 53, was glad to take his place. He works as a pipefitter all winter but "when the first spring weather comes, I have to go. I love the road. There's something new at the top of each hill." This was his first trip this year, and he still had burns on his fingers from his last pipefitting job. He had last been to Washington in 1978, when he drove a group of junior high school students. On this visit, he would find the city much different from the one he had remembered, its streets and traffic patterns more crowded and confusing, bus parking spaces virtually impossible to find, new signs warning "No Trucks or Buses."

But now, on the highway in the morning, he was happy. He drove past the familiar signs: Red Star Fireworks Factory Outlet, Quincy's Family Steakhouse, Abbotts Farm Apples, Big Red Chewing Tobacco. The bus stopped several times on the way to Washington. The group ate lunch at the McDonald's just off I-85 in South Hill, Va.. They walked quickly around Williamsburg and had dinner in the cafeteria there. They used the facilities and looked at the souvenirs at the Speed and Briscoe Truck Stop in Ashland, Va., where a sign advertised "Free Pair $7 Mirrored Sunglasses With Any Pair of Western Jeans." Allen Cox bought for his mother a silver demitasse spoon engraved "South Carolina."

It was about 11 p.m. when the bus arrived at the Sheraton Washington at Woodley and Connecticut. The glass and brick hotel towered 10 stories high. The students, like many of the guests, would get lost among its corridors, which wind past 1,505 rooms, four restaurants, two cocktail lounges, one gift shop and one game room. Everyone was given rooms on the ninth floor except for the bus driver, whose room was on the seventh floor. There was no button for the seventh floor on the first elevator he entered. "I don't like this," he said, exhausted and frustrated. "I like the kind where you can just drive right up and go inside."

Mrs. Glenn, who shared a room with Mrs. Dobson, set curfew at 15 minutes after midnight. Everyone stayed in the rooms, but not everyone went to sleep. Some stayed up for hours, talking about all that they had seen so far.