Three Metro trains broke down in the heart of the morning rush hour yesterday to bring long delays to thousand s of already confused commuters who had been forced off their buses and on to the trains for the first time.

The breakdowns, compounded by long lines at fare gates and natural confusion over something new, made a shambles of Metro operations on the day it realigned 180 bus routes to reed the subway.

"They ought to scrap the whole thing, fill in the hole and give us our taxes back," a silver-haired matron yelled to an official as she searched for her train at the two-level Rosslyn station. "You stand upstairs and wait, then you come downstairs and wait."

Metro, forced by the breakdowns to detour "good" trains around stalled ones, had to bring Washington-bound cars in on Virginia-bound tracks. Only one announcement was made in the Rosslyn station to that effect despite the fact that people who had not heard it were arriving every minute.

At least 3,000 people were captives for 20 minutes in jam-packed trains backed up behind a stalled one at the Foggy Bottom station platform. One of those trains was in the long tunnel under the Potomac River, and to be stuck there is an event that frightens some people.

There were long lines at the automatic fare-collecting machines during both morning and evening rush hours. At stations like McPherson Square, where there is not enough equipment, Metro officials let some people in without farecards, the magnetically encoded ticket needed to enter and leave the subway. Other Metro officials would not let them out without a hassle at the end of their rides, however.

Those commuters most irritated yesterday appeared to be the one who had been forced off fast, reliable bus service and into the tunnels on gleaming trains that appear to show great promise but have been unreliable to a fault from the moment expanded subway operations began July 1.

Bill Kemper, of Annandale, expressed the bitterness that many others felt. At the end of the day, as he left the Pentagon Metro station, he redeemed his farecard for 20 cents and told a reporter, "I'm going to buy a small car." His old bus trip in the morning, he said, took 50 minutes. Yesterday, using the bus and the subway, his trip to work took him 1 hour and 45 minutes, he said.

Metro train control personnel themselves conceded it was one of the worst days they have ever had. There were two breakdowns on the National Airport-Stadium Armory line between 8 and 9, and a third on the Dupont Circle-Rhode Island Avenue Line at about the same time. A total of 10 trains scheduled during the morning rush were never dispatched because of delays.

"It's the first time we've had to [WORD ILLEGIBLE] trains on both lines at the same time," one fofficial said.

In the evening rush hour, a train broke down in the Eastern Market station on the route to Stadium-Armory. Virginia-bound commuters were not affected, but service east of Capitol Hill to the Stadium was reduced from intervals of 5 minutes to intervals of 20 minutes for almost an hour.

All of the failures yesterday were attributed by Metro officials to problems in the Metro cars' complicated braking systems. If any one of several sensitive detectors on the cars does not like what it detects in the brakes, it locks the brakes and prohibits a train from leaving the station.

The brake system is being completely refitted on all Metro cars to reduce the problems, Metro officials said, but only about half the fleet has been refitted. Sticking doors, the most obvious problem early in Metro's expanded operations, have all been readjusted. There were a few sticking doors yesterday, too, but no major delays because of them.

The problems could not have come at a more inauspicious moment for Metro, which is continuing its efforts to eliminate parallel bus and subway service and thus save money.

The 180 bus routes changed yesterday brought commuters into Metro stations at National Airport, the Pentagon and Union Station in the District of Columbia. Metro has estimated that 15,000 commuters would be affected.

Metro has started that changeover on Aug. 1, when 210 bus routes were changed along with the travel habits of about 25,000 commuters.

The changeovers and curtailments were forced by locally elected area governments, which are financing a Metro bus and rail operating deficit of $76 million primarily from politically sensitive, local property taxes. The elimination of parallel bus sevice is projected to save Metro between $4 million and $5 million this fiscal year.

The changes have been forced on an expanded subway system that has bugs in both trains and automated fare collecting equipment that Metro has had two months to correct.

With summer-time crowds and only half of the bus changeover completed, Metro got through August with only a few delays, although there was one monumental foul-up when a control panel switch was left in the wrong position and ruined a morning rush hour. A flood in the tunnels caused by a construction accident forced Metro to curtail operations for four days two weeks ago.

But yesterday morning, Labor Day was past and the full crush of Washington's morning commuter load was placed on the system. It developed a serious congestive cough.

By 8 o'clock yesterday morning, people were standing four deep at the Pentagon platform waiting for a train. There were lines of people 20 deep waiting to get through the fare-collecting gates. Although the gates are reversible, only four of the 14 were admitting passengers; the rest were discharging them.

Finally, in a station that was filled with Metro brass from general manager Theodore Lutz on down, somebody made the decision to reverse most of the gates. That cleared the problem. In the evening, the gates were reversed before the crush hit.

Eight-car trains, the longest Metro can run, whizzed into the Pentagon Station with precision, and left with standing loads. By the time they got to Rosslyn, another major Metro bus terminal, there was little room on the train for the crowds of people waiting there.

Rosslyn commuters, pushed out of their buses on July 1, have been accustomed to mostly empty trains. They had to fight for standing room yesterday.

The trains labored on, but at 8:10 one of them quit in Foggy Bottom with two tied up behind it, and the morning rush hour was lost.

Passengers on trains stacked up behind the stricken one complained later that they were given a dearth of information over the train's speakers and that the information they got often was optimistic. "We'll hold for about 3 minutes," one announcement said, but the train did not move for 20 minutes and there were no other announcements.

The other morning breakdowns, at McPherson Square and Dupont Circle, only compounded the problem.

There were unhappy people everywhere, and not just because of subway breakdowns. District of Columbia commuters who use the heavily traveled Benning Road and H Street bus lines were encouraged, but not forced, to get on the subway yesterday at Union Station. Most of them declined.

Their buses loop through a new terminal four floors removed from the subway stand stop. D.C. residents for the most part transferred to other buses rather than go down four flights of escalators to the subway and pay another fare.

Because of Metro's Byzantine fare structure, round trip costs for riders using the bus and subway are about the same as a bus-only round trip for most Virginia and Maryland residents, but 30 cents to 40 cents more for most D.C. residents.

At the end of the day yesterday, as Annandale commuters rolled home on the Shirley Highway bus lanes after transferring from the subway at the Pentagon, they traded Metro horror stories.

"For seven years, I have made a conscientious effort to avoid New York," said Richard Helmick, a communications lawyer. "So what do the do? They bring New York to us."