The wake-up calls came at 6 o'clock for the 29 seniors from Blue Ridge High School. It was the first morning of their class trip to the nation's capital. They had arrived late the night before on an old silver bus, after a 500-mile journey from the foothills of Hogback Mountain in South Carolina.

Now, Washington awaited.

In the next 48 hours, they would rush through the tourist's Washington, the one seen by some 100,000 visitors each week at this time of year. Their indefatigable escort was Sarah Glenn, English teacher since 1946 and devotee of the federal monuments and museums to which she leads the seniors each year.

Theirs was a Washington of endless facts, ticked off with authority by a succession of professional guides: The Washington Monument is 555 feet, 5 1/8 inches tall; the elevator ride to the top takes 70 seconds. The Library of Congress has 20 million books and pamphlets in 60 languages, more than 35 million manuscripts, 10 million prints and photographs, almost 4 million maps and atlases. The Washington Cathedral is the sixth largest cathedral in the world; its organ has 10,531 pipes. The Bureau of Engraving and Printing employs 3,500 people who work 24 hours a day turning out currency with a face value of $20 billion a year; the average life of a dollar bill is 18 months. The Museum of Natural History holds the Hope Diamond, which is, at 44.5 carats, the largest blue diamond in the world.

The students from Blue Ridge would learn more facts at the Federal Reserve, National Zoo, Museum of American History, National Archives, Jefferson Memorial, Lincoln Memorial and Supreme Court--all between 7:30 a.m. last Thursday, when the old silver bus rolled out of the Sheraton-Washington parking lot, and 10 a.m. Saturday, when it left the city via the 14th Street bridge. They would fortify themselves on this fast-paced budget tour at two different Sholl's Cafeterias, McDonald's and the cafeteria in the basement of the Museum of American History. They saw two movies: "To Fly" and "Living Planet," both at the Air and Space Museum. The evening entertainment was more touring on the old silver bus.

The city would enchant the seniors and their three faculty chaperones from Blue Ridge High, which has 620 students and 32 teachers and is located 10 miles from the nearest town (Greer, "Heart of the Piedmont," population 10,000). As Rogene Gaddy, drum major and daughter of a schoolteacher, said on the final night: "No one tells you about all the marble."

Joey Hipp, who wants to be an engineer, couldn't restrain himself when he saw the inside of Washington Cathedral and used up all the film in his camera. "It overwhelmed me," he said. "I got a wild hair up my back and took 11 pictures."

Allen Cox, centerfielder on the champion Blue Ridge baseball team, was dazzled by the sight of thousands of fresh green bills being produced at the Bureau of Engraving and Printing. "I'd like to come back here and get a job making money," he said.

Doris Dobson, the guidance counselor at Blue Ridge, who had last seen Washington 31 years ago, on her honeymoon, kept saying, as she looked out the bus window: "Look at the tulips! I've never seen so many tulips!"

But not everything would be as it seemed, or as they had expected. Their U.S. senator, Strom Thurmond, showed up for his photo session with them on the Capitol steps looking, they thought, decidedly not like a senator. He had a Band-Aid right across the middle of his nose. "He cut it pruning trees in his backyard in McLean," said one of his aides.

The Library of Congress, with its imposing bronze doors, towering gold-edged ceiling, elaborate murals and marble staircases, was beautiful. But Roger Fowler, who wants to be a peach farmer, like his father, wondered: "Where are the books?"

Even the people on the streets, who also became a part of the students' Washington, were perplexing. In the morning, every other woman marching down Connecticut Avenue seemed to be wearing sneakers with a fine suit or dress. "We thought it was a new style. We were going to go back to school wearing tennis shoes," Donna Emery, the school newspaper editor, said. She and her classmates learned the sneakers were for walking to work and would be shed at the office for the footwear of the business world.

From across McPherson Square at the corner of 15th and K streets NW, they saw a bright red, black and yellow facade and thought it had to be the entrance of a Wendy's--one of their favorite restaurants back home. But, alas, inside there were no hamburgers. The facade turned out to be the Ellwest Theatre, featuring a movie titled "Gang Bang."

And what looked like veal parmesan at the Senate cafeteria turned out to be, under the tomato sauce and cheese, eggplant parmesan. Hardly anyone had ever eaten eggplant; no one felt like eating it now.

But the biggest disappointment came on Thursday, when the White House was closed to the public. The reason, according to a White House spokesman, was that President Reagan was entertaining 90 journalists in the state dining room, which is part of the official tour. The journalists' lunch: cold curry soup with cheese twists, roast tenderloin of veal, chateau potatoes, strawberry mousse. Friday the mansion was open again. But the line of tourists stretched interminably, too long for a group with one day out of a two-day visit remaining. So the students' closest look at the White House was from the windows of the old silver bus.

The prices were startling, beginning with their hotel--the Sheraton Washington, which Mrs. Glenn said they chose because they couldn't find rooms anywhere else when they began checking last December. The bill for three nights in one single, two twins, two triples and six quads came to $3,177.90. That included a $70 charge for "porterage"--Sheraton language for what the bellmen do with the luggage. The Blue Ridge group, said Mrs. Glenn, would have preferred to save the money and carry their own bags. But "porterage" is almost always included on group tabs, according to a Sheraton spokesman. The room service menu included $8 for a bowl of pretzels or potato chips, $4.25 for a continental breakfast, $3.25 for a giant chocolate chip cookie and coffee.

No one had room service at breakfast. But the students from the school outside Greer--where $7.25 buys an excellent filet mignon dinner with baked potato and salad at the Lakeview, considered to be one of the best local restaurants--didn't find the prices in the Sheraton restaurants any more in line with their budgets. On the first morning, Veronica Byrd, the class track star, who dreams of making the 1984 Olympics but plans after graduation to learn the sheet-metal trade at a technical school where there is no girls' track, went with two friends to the Courtyard Cafe and came away shocked and slightly crestfallen.

"The french toast was $2.50. Orange juice cost 97 cents!" she said. "I asked the man how much the syrup was, and he just looked at me and said 'Nothing.' "

Veronica had already written her first postcards. To her mother and father and brother and sister, she sent a picture of Robertson's Windmill in Williamsburg, where the bus stopped on the way to Washington. " . . . I miss you all! I actually saw this windmill. It was a beautiful place. I wish you all were here." To her boyfriend Kenneth, who works at the Greer Mill, she sent a picture of Duke of Gloucester Street: "I saw this when we stopped in Williamsburg. Really. I walked down this street. I even got a four-leaf clover . . . "

By 7:30 a.m. Thursday everyone was aboard the ungainly 39-passenger, 1953 silver bus that is known as The Baby Elephant. Driver J.C. Kimbrell, from Spartanburg, S.C., headed down Connecticut Avenue, past the Washington Hilton. "That's where the president was shot," Mrs. Glenn said.

Their first stop was at 8 o'clock at the Bureau of Engraving and Printing, where a gray-haired man with a green canvas shoulder bag got on and held out a stack of picture postcards: "All your favorite scenes. Fifteen for a dollar." Mrs. Glenn, the veteran Washington tour leader, didn't even look as she commanded him off the bus with a firm "No, thank you."

The FBI was scheduled for 9, but the line was too long for them to make their next appointment--an hour later at the Federal Reserve--so they postponed it until after their 11:30 a.m. tour of the Washington Cathedral and went instead to the National Archives. That didn't work out either; the archives didn't open until 10. Next they tried the Museum of Natural History, but that, too, opened at 10. They planned to return after dinner until a guide informed them that summer hours were not in effect this year because of budget cuts and the museum would close at 5:30. ("President Reagan could cut back on his own staff," said a disappointed Mrs. Glenn. "And Nancy could get a broom in her hands.") By this time, they had to be at the Federal Reserve. Then through the lunchtime traffic jams on Massachusetts and Wisconsin avenues to the Washington Cathedral.

All this time Kimbrell had been driving in what seemed like endless circles as he encountered one-way signs that seemed to appear out of nowhere and searched fruitlessly for a parking space. He would become more and more frustrated on this trip, his first since 1978. "It's changed," he said. "Everything's all torn up. The police won't let you park anywhere. The local buses get all the parking spaces."

At the cathedral, a woman in a long purple robe met the group with a cheerful "C'mon in, South Carolina." Debra Whiteside, who was voted "best all around" student in her class, gazed up at the stained glass, sparkling in the sunlight. "Now, that's beautiful." Doug Carson, who will join the Army after graduation and is so shy that he never corrected the teachers who called him Carl most of the year after his name appeared incorrectly on a computer printout, walked through the cathedral, characteristically silent and enraptured.

The students went to the Museum of American History for lunch and browsing. Tracy Jeffeaux, who marches in the Blue Ridge band, talked about the woman she had seen sunbathing in a bikini in a park near the White House. "We would never sunbathe in a public place at home."

On the way to the Museum of Natural History, Mrs. Glenn warmly greeted a couple on the street. She didn't linger. "They were the Steeles," she said after she had said goodbye. "They're from Greer." Tracy wasn't nearly as casual about the idea of meeting friends from home in Washington. "That's like seeing someone you know at the South Carolina-Clemson game," she said.

After the museums, the group boarded the bus and went to Arlington Cemetery, missing the Memorial Bridge exit on the way and ending up briefly in Rosslyn. The cemetery has special meaning for Mrs. Glenn, whose husband Fred was badly wounded in World War II. "I always cry at Arlington Cemetery," she said. The students were also deeply moved. Tracy, looking down from the hill at the rows and rows of white tombstones, said, "Bless their hearts, every one. It's like a holding place--heaven on earth."

"Beautiful," Veronica Byrd said. "Sad, but beautiful."

The group ate dinner Thursday night at the Sholl's Cafeteria in the Esplanade, where the $1.65 special was creamed ham and macaroni. They next visited the Air and Space Museum, where they stayed until closing time at 9. They had planned to proceed to the Washington Monument, but driver Kimbrell, who had spent the day behind the wheel of the bus, said he was too tired. They went back to the Sheraton, where most of the students watched TV, shared the snacks they had brought from home and walked around the 10-story hotel.

The next day Roger Fowler reported on the adventure of Thursday night. It had been about 10 p.m. when he, Allen Cox and his girlfriend Candace Lynn (voted the most school-spirited boy and girl in the class), Darlene Land (voted, for her singing talent, most talented) and a few others ventured out of the hotel and across the street to the subway stop at Woodley and Connecticut.

"We went down and stood there and watched a train come in," said Roger. "We wanted to take it, but we didn't. We heard there were gangs down there. We were afraid we'd get lost or mugged." They emerged from the underground, took a walk around the block and returned to the safety of their rooms on the ninth floor.

Roger said they didn't go further because they were afraid something might happen. The wide-eyed students from South Carolina might look like easy victims, he explained. "People can tell we're not from here. We're always looking around at everything we see. But everyone else just walks right past." He and his classmates looked out for each other in the city they viewed as strange and dangerous. No one rode the elevators alone. The boys escorted the girls across the streets, to souvenir shops and ladies' rooms. Everyone, chaperones and students alike, watched over the student who attends special education classes. They made sure she got what she wanted at meals and wasn't ripped off at the T-shirt stands along the sidewalk.

On the last day Sen. Strom Thurmond effusively greeted the students on the steps of the Capitol.

"Just call if I can ever do anything for you," he said.

Donna Emery said afterward, "I felt like saying, 'Get us into the White House.' "

That night they visited the Lincoln and Jefferson memorials and viewed the city from atop the Washington Monument.

At the Lincoln Memorial they were solicited by the same postcard salesman ("All your favorite scenes; 15 for a dollar") whom Mrs. Glenn had turned away the day before. Turned away again, he delivered a woeful speech:

"I started doing this 20 years ago at Arlington Cemetery--before John Kennedy was shot. In those days I sold a zillion postcards. I gave away a souvenir pin from Hong Kong with an emblem that said 'Nation's Capital.' It was a good package for $1. Now I can't make a living working 24 hours. Everyone's in too big a hurry to get to the souvenir stores . . . "

He was still talking as the old silver bus moved off for the Washington Monument, which the 29 seniors had seen from a distance for two days. They waited in line more than an hour. It was cold. A few students suggested they give up and go back to the hotel. But Jimmy Tooley, fullback on the football team, said, "We can't miss this. We've been leading up to it the whole time." They reached the top around midnight. "Oh, Doug, look at that," Veronica said to Doug Carson as they looked out the window toward the Capitol, with its dome gleaming in the distance.

Saturday morning they ate their last breakfast here--at Sholl's. The Blue Ridge senior class trip was pronounced a great success. Roger Fowler said, "I'd like to come up here someday with my children. I'd show them that cathedral." But he and his classmates, with few exceptions, swore they could never live here.

"It's too fast," Veronica said. "Too high, and too fast."

"It's not home," Tracy said. "We're from the country."

And soon the old silver bus disappeared down 14th Street, across the 14th Street bridge, out of the city and home--to the hills of South Carolina.