An electrical power outage and a train breakdown combined yesterday morning to snarl service on Metro's Orange and Blue lines and delay thousands of commuters and tourists for up to two hours.

The unusual procession of events was felt most serverely by people coming from Prince George's County, Far Northeast Washington and Capitol Hill to downtown Washington. Many of them were trapped in trains or stations for as much as an hour while Metro attempted to solve the problems.

Riders from Virginia were also confrnted with delays in service as they had to wait longer than usual for trains during the series of incidents that started at 8:01 a.m. and did not end until early afternoon.

The biggest problem, and the one that led to a succession of other problems, was the failure of a Potomac Electric Power Company cable into Metro's Cheverly station, on the Orange Line in Prince George's County.

That failure did not stop the trains, but it turned off their signals. From the Station-Armory station in the District to the New Carrollton station at the end of the line.

In the absence of signals, the trains will not go faster than 15 miles an hour no matter what the operator does. Therefore, trains crawled from New Carrollton to Stadium Armory in 25 or 30 minutes yesterday instead of the usual 13.

That meant that trains were delayed getting back downtown and into Virginia. To make matters worse, switches in Metro's main turnaround track, located between Stadium-Armory and Minnesota Avenue, had gone on the blink minutes earlier.

To compensate for those two problems, Metro discharged passengers on a New Carrollton-bound train at the Smithsonian station, then tried to return the train to Virginia through a crossover switch located between Smithsonian and Federal Triangle. That train got halfway through the switch when its brakes locked. The Blue-Orange line was thus effectively blocked in both directions, because the train came to a halt on both tracks as well as the crossover.

Two downtown-bound trains were trapped behind that train and one of them carried a man who became ill.

Joan Shycoff of Bowie, a passenger on that train, said the situation was "most upsetting. . . . There was no emergency button and the doors don't open between stations. Children on the train were really frightened because we were just sitting there in the tunnel and this man was obviously ill." The air conditioning worked intermittently, she said, "but we were packed in and it got hot."

Emergency call boxes, marked in very small letters that are invisible from more than a few feet, are located in the ends of each car. Metro records show that someone did call the train operator and report the sick passenger.

Anthony Stefanac, the subway's general superintendent, said the train operator asked if medical assistance was needed and was told no. The train stuck in the Smithsonian station was moved up to the train stuck in the switch, and the train with the sick man was moved into the Smithsonian station.

The man was taken to Georgetown University Hospital, where he was examined and released.

It took an hour to clear the switch. Pepco got the power back on at 12:40 p.m., and the railroad returned to normal about 1:20 p.m.

A Pepco spokesman said the power outage may have been related to problems left over from Thursday night's storm, when a lightning strike knocked out some power cables to Metro and delayed homebound commuters to New Carrollton.

Metro tried to substitute buses along the subway line, but only four buses ran. Many passengers, in calls to The Washington Post, complained that announcements in the stations and on the trains did not detail the extent of the problem or the time it would take to solve it.