The swelling crowd of Sunday excursionists milled around the brightly lit platform in confusion, pushing into the overcrowded orange and gray subway cars just like practiced New Yorkers, Londoners or Parisians.

To inaugurate the new Rome "Metropolitana," hundreds of thousands of hand-holding couples, curious teen-agers and entire families -- with children, grandparents, thermos bottles and sandwiches -- had jammed into the subway that city politicians had been promising for two decades.

"After so many empty words, I frankly didn't think I'd live to see it," said an elderly pensioner.He had taken the 25-minute ride once from start to finish, and again to inspect each of the 21 spartan, unadorned stations and to try out the steep escalators.

This weekend's inaugural crush of 1.2 million people led subway officials to temporarily shut down some stations as a security measure.But it convinced them that the line, which connects the eastern edge of the city to a major downtown commercial area just west of St. Peter's Bisilica, will be a success.

Rome officials estimate that the new, fast six-car trains (capacity 1,300, running every four minutes) will serve 80 million Romans each year, halving to 26 minutes the traveling time downtown for residents of southeastern Rome. They also hope that the new rapid transit system will ease surface traffic congestion.

But according to some urban planners, this weekend's opening will not obliterate the muddles of the past. "It is appalling to think that it took twice as long to build this 14-kilometer (9-mile) single subway line as it did the Suez Canal," said urban studies expert Antonio Cederna.

The A Line, furthermore, represents only a fraction of the original 65-mile project that first appeared on drawing boards here in 1962. It reportedly cost more than $375 million (more than $41 a mile); that is almost 10 times the original budget of $40 million.

Part of the problem in completing a project that was first authorized in 1959 was the intrusion of the subway near the archeological remains of ancient Rome. This made it necessary to dig to depths of more than 150 feet at some points. At one station site a Roman bath was discovered. At another point an underground lake came to light. The jungle of underground utility networks -- gas and water pipes, telephone lines and a plethora of electricity systems -- made progress difficult if not, in some spots, almost impossible.

But according to Cederna and other observers here, political infighting, bureaucratic confusion and disregard for the problems of public transport were primarily responsible for the "exasperating slowness" of the work on the subway.

Since the initial approval of the subway project by the Chamber of Deputies' Transport Commission on Nov. 11, 1959, there have been 23 Italian governments and 10 different mayors of Rome.

The A Line begins on the southeastern periphery of the city just beyond Cinecitta, the movie studio once known as Hollywood on the Tiber. It runs past the central train station, under the well-known Piazza di Spagna (which is connected to Via Veneto bby a 400-yard underground moving sidewalk below the Tiber River) and ends in the Prati section of Rome.

At the station the new line links up with Rome's elder subway, a 6 1/2-mile stretch of track begun by Mussolini to service the outlying World's Fair area in the EUR suburb and the Ostia beach resort. It was completed in 1955. City officials are planning to begin work later this year on an extension of this subway, which would become the city's B-Line.

The two lines, meeting at the central train station, will eventually dissect the city in an enormous X. Two other lines, C and D, that would give Rome a subway network comparable to other major cities of the world, are now unlikely to be built. "We just can't afford it," said a representative of the city's transport office.

The new low-cost subway -- a single ride costs 25 cents and a monthly pass sells for only $5.65 -- is expected to reduce car traffic in this city of 3.5 million people by up to 15 percent. It may also help to ease traffic by eliminating the need for many buslines that serviced the same route.

Critics of the new transit system, however, point out that city planners have left several important things undone. A giant car-park at the subway's southeastern end is only a fraction of the necessary size. And proposals for the construction of a huge underground garage at the other terminal were ignored.

Down below the city's surface, however, riders on the new Metropolitana appeared entranced.

"It's a great step forward," said a woman pushing a baby carriage. "What difference does it make that it took so long? After all," she added smiling, "Rome wasn't built in a day."