The Metro Subway's new Blue Line from National Airport to RFK Stadium officially was dedicated by the politicians yesterday, but the masses ignored the ceremonies and jammed onto the trains instead.

The trains responded during the afternoon with three breakdowns that caused delays of at least 20 minutes each time and numerous minor glitches - such as sticking car doors - that cut seconds and minutes from Metro's scheduled running times.

Very few people seemed to care. Thousands of people rode the trains fromt one end of the Blue Line to the other, then turned around and rode back again."Nobody ever gets off," one Metro official said in exasperation. "How can we put more people on if nobody will get off?"

Indeed, not getting off seemed what a number of people had in mind. They came in family groups yesterday, casually dressed, carrying cameras. Some wore the Washington Underground t-shirt that is becoming a popular item, and many more wore the "I'm Not a Tourist, I Live Here," model.

When they got to National Airport, they stood on the elevated platform there and watched the planes take off and land. Some of the more serious photographers even set up tripods.

Metro put every available car in its fleet into service yesterday and ran seven six-car trains and five four-car trains on the Blue LIne. It was not enough. The first train from National Airport yes- terday, a six-car model had a standing load in all cars within 10 minutes and seven stope. It was that way through the afternoon, until a slight lull hit before the expected crush on the system came for the evening fire-works on the Mall.

The biggest troublemaker for first day users of the Metro on Friday had been the automated fare-collecting system that requires the rider to purchase a magnetically enroded ticket to ride the train. That was abandoned for yesterday, and patrons could ride for 50 cents, which they deposited in barrels set up at station on entrances. The automated gates were locked open yesterday, so across to the station platforms was simple matter.

Access to a seat on a train was something else again. Passengers would wait for 10, 15, 20 minutes for a train to come, and when it got there, it would be full. There were occasionally amusing scenes.

At Metro Center shortly after 6 p.m., a throng began to build on the platform for the National Airport line. Four trains went in the opposite direction - toward the Stadium - and none came for the Airport crowd, which continued to build.

Finally, a train pulled in to great applause.

The applause turned to catcalls and some people pounded on the front doors of the train when they realized it was jammed full. Those who were standing on the platform at the other end of the six-car train however, were not at all disturbed. There were planty of empty seats on the last three cars.

The strange headways (spacings) between trains are caused by a number of factors. Metro officials explained, including all-new equipment, the extraordinary loads overstressing the cars, and inexperience on the part of some train operators.

"It will improve in time." said Arthur Seeger, a superintendent in the Metro control center. "You're looking at us in our infant time and we are struggling. We're asking for kindnes."

One train in the early afternoon limped from the Smithsomian station to Crystal City in 45 minutes, a trip that is supposed to take 14 minutes. Every time the train would stop at a station and take on even more passengers, the operator would have to close the doors two or three times before the electronic sensors were satisfied that the train was secure to operate.

Then it would creep along for a ways and stop in a tunnel. "I'm sorry folks," the operator said as the train stood still in the tunnel under the Potomac River, "there's a broken-down train in front of us and we can't get too close."

The train lurched forward again for a few feet, then stopped. "Daddy, is there a red light?" a small boy asked his father.

"Nah, this is the sort of thing Metro's becoming famous for on the Fourth of July," the father replied. His answer was of no help to the child but underlined one of the public relations problems Metro has if the trains don't start running smoothly soon.

On July 4, last year, thousands of people were stranded on the Mall for hours after the Bicentennial fireworks when promised Metrobuses either did not show up or were swamped in traffic.

At National Airport yesterday, people in Lines a block long and five abreast meandered underneath the platform waiting for trains back to Washington. Metro officials limited the number of people on the top platform to what it could reasonably hold. Extra buses were dispatched to relieve the National Airport load, but most people declined the bus ride and waited for trains.

Elizabeth Saldanha, a graphic, designer and photographer from India, said she was taking the train "just for the ride . . . I felt very much at home. It reminds me of Bombay, because it's crowded always crowded."

Another in the crowd, Brada Panther, secretary with the Federal Reserve, said. "I don't mind" the wait. "I'm not in rush to get anywhere.

Adding to the holiday mood yesterday were four traditional-looking July 4 ceremonies dedicating the Metro. The big one was in Crystal City, were about 350 people sweltered in the 90-degree-plus heat for 15 minutes while waiting for some Metro officials to arrive on that slow train.

One of the earlier trains obviously had run well, however, because it carried Acting Maryland Gov. Blair Lee III to the ceremony. "It works," he declared. "This is a good investment."

Lee and Mayor Walter Washington both went out of their way to praise the subway and apparently some of it was for the benefit of Virginia Gov. Mills Godwin, who has not always been perceived as a friend of Metro.

Godwin himself said that the rest of the state joined "with you and the rest of Northern Virginia in joy . . . over a new system of transportation for the people of this area."

In his prepared remarks, which he did not deliver because of the heat, he said. "Virginia's position and that of this governor has consistently been that the Metro rail concept was a vital part of the solution to the transportation problem presented by the orientation of Northern Virginia to the nation's capital city."

There also were ceremonies yesterday at the Eastern Market Station in the District of Columbia at the Smithsonian station in the Mall, and at the Rosslyn station.