Eighteen-year-old Nicholas Ratner was in line by 9 p.m. Friday to make sure he got on the first low-cost, no-reservation Laker Airways "Skytrain" flight to London.

He could have come to the new Laker Travel Center here at 9 a.m. today or later, and still have gotten a ticket on tonight's inaugural flight.

But Ratner, who had hitchhiked and taken a bus from the West Coast with a friend to be on this first flight, wasn't sorry he had gotten here early.

"Andy Warhol once said everyone should be a celebrity and get on television for 15 minutes in his life. I think he would be proud of me," he said. Ratner gave at least two dozen interviews through his 55-hour wait until he purchased his ticket - the first - at 4 a.m. this morning.

The sale culminated a more-than-six year quest by Freddie Laker, the ebullient head of Laker Airways, to offer what he calls the "forgotten" men and women scheduled airline service they can afford.

Beginning today, Laker will offer travelers a flight to London from New York for $135, and a flight back for 59 pounds (about $102) to the first 345 people to line up ans pay their money at each end. The same plane leaves London at 5:30 p.m. London time arrives in New York about 8 p.m., loads up by 11 p.m. and returns to London by 10 a.m. the next day. Tickets for each day's flight cannot be sold before 4 a.m.

Many people think Laker's innovative, low-cast, no-reservation service will revolutionize transatlantic travel, making it as convenient as the Eastern shuttle between Washington and New York. Already, his new service has led the "club" of scheduled airlines, as Laker calls them, to respond to his air faes with limited but similar offerings (just 20 dollars more round trip) - a feat they have been contending for years was not possible.

The sale of the first ticket this morning to Ratner, a recent high school graduate who cooked and washed dishes all summer to earn his fare was greeted by appluase by the cheerful crowd of 170 others travelers waiting to buy tickets. About 100 of them had been there at least 12 hours.

Ratner and other purchasers were presented with certificates proclaiming them passengers on the first Laker flight from New York to London, signed by Freddie Laker.

"Nick's the answer to a trivia question now," John McIntyre, a 25-year-old counselor for emotionally disturbed children, said. McIntyre is on his way to Ireland. His 44 pounds of luggage was taken up almost exclusively by the bicycle he is talking with him.

Georgette Bartell, 30, was a nurse at George Washington Hospital until she quit Sept. 14 to take a long-planned six-month trip to Singapore and Malaysia. She found that a trip there vua Laker to London was much less expensive than the alternative route through the West.

Chuck Adelman, 31, from San Francisco is "on an extended goofing-off period," he said. He took the bar examination in California in July and decided to take a trip before the results are in. "I'm so much in debt, what's the difference?"

Although the crowd was predominantly young - in their 20s and 30s - with many carrying sleeping bags and backpacks, members of the older generation were represented as well.

Larry Carke, 54, a composer and instructor at Santa Rosa Junior College where he hopes to write music during a year's leave of absence. He heard about Laker six months ago. He cause he wanted to support someone who was doing something unusual and wanted to be on the first flight be-innovative, he said. "It became a cause with me," he said. "It's also an adventure."

Many of the cost-conscious travelers were not Americans. Baly Yves, a 35-year-old black, French chef in New York, was going to see his family in Franch via London. "I would not have gone at all," he said, "were it not for the Laker flight.

There was one family in line through the night. Robert and Irene Cave were taking their three boys back to Cambridge. England, after a four month stay in the U.S. The Caves had planned to stay a year, but Cave, a plasterer, found himself out of work in Norwalk, Conn., where they had settled.

"I've had too many knocks here," he said. "I can be out of work at home too, but my friends are there." They started planning for the trip the minute they read the Laker would be starting its low-cost service today. With thefive of them. Cave estimated he would have to spend another $1,000 to get home were it not for the Laker flight.

Although there were up to 20 people in line at times on Saturday, people began arriving at the Laker Travel Center more steadily Sunday morning.

People were waiting outside in the dreary, drizzly, chilly and windy weather until 4:00 p.m. Sunday when Margaret Newman, secretary of Laker's North American manager, Charles Maxwell, took pity on the increasing numbers of drenched prospective travelers and invited them in. Workmen were busy laying carpet, painting walls, moving in counters and chairs throughout the day.

Inside, a line formed in a most cheedful and benign fashion. Those waiting were offered hot coffee and cookies throughout the night. Most people sat on the floor, read newspaper, played cards and backgammon, ate, and wandered around and talked to each other.

At 9:00 a.m. the center was "officially" opened and Gordon Booth, British Consul General and Director General of the British Trade office, cut the ribbon - a green ribbon for "Go", Laker officials said. Champagne was served.

Everything went smoothly. "I'm quite happy about it," Maxwell said. He added that he would much prefer to be able to accommodate each passengers who wanted to travel during the next few weeks than have a throng of passengers who couldn't all get on, thus discouraging others from trying the new service.

Tickets were sold throughout the day. By 6:10. 19 tickets were still available.

The first Laker flight from London left with 276 passengers on board, plus Laker himself, who will turn around and board the flight back to London after a two-hour stay here, using an unused pullout "jump" seat the cabin attendants use if the 345 seats are filled.