A major electronic failure forced air traffic controllers to shut down the radar system at Baltimore-Washington International Airport today, delaying flights for much of the day and disrupting travel plans for hundreds of passengers.

Delays of almost two hours were reported as controllers guided pilots by radio and the slow service prompted confusion in the airport terminal, but airport officials said there were no dangers aloft.

"Safety was not derogated one iota," said BWI tower manager Mike Sarly.

He and other officials said a key electronic component failed late Monday night, crippling part of the radar system. Technicians tried unsuccessfully to repair or replace the component during the night when air traffic was minimal.

Officials said they then took the unusual step of closing the entire radar system at 7 a.m. today to make the repairs. The system remained down until 12:53 p.m. when workers completed the repair job and flights resumed their normal schedules by 2 p.m., officials said.

"I don't recall this particular kind of thing happening at any airport recently," said Federal Aviation Administration spokesman Fred Farrar.

During the radar shutdown, air traffic controllers used special "flow control restrictions," limiting outgoing flights and separating incoming planes by 10 to 12 miles, rather than the standard three miles, Sarly said. It was these restrictions that caused the flight delays.

The fact that it was a relatively clear day "helped some," he said, and allowed pilots to proceed with greater safety as they approached the airport. The controllers continued their work generally in the same manner as when the radar is working and no extra flight controllers were needed to help with the traffic, he said.

Farrar said that in general when a radar breakdown occurs, air traffic controllers use radio contact with pilots to ensure that they keep the greater safe distance from other planes and to monitor their locations. In this standard procedure, he added, they instruct incoming pilots "to fly to a certain point, and when the pilot radios back that he has reached that point, the controller can call in the next plane, and so on," thereby keeping a safe separation between the planes.

Inside the terminal, some passengers waited wearily for their flights while others lined up at pay telephones to alert friends and families of the delays.

"This is our first airplane flight as a family, so we hope it isn't always like this," said Linda White of Manheim, Pa., as she waited with her husband, Donald, and their children, Brynn, 5, and Megan, 8, for an 11:30 a.m. USAir flight to Walt Disney World in Orlando, Fla. "We've been planning this trip for a year, so it's kind of hard to sit here and wait."

BWI is the 28th busiest airport in the United States, with more than 122,000 operations annually, according to the FAA, and is far less busy than National Airport with 191,000 flights a year or O'Hare Airport in Chicago, the nation's busiest, with almost 600,000.

Sarly said when problems arose Monday night, the airport's primary radar system, showing the position of planes on the traffic controllers' screen, was functioning properly, but a secondary system failed to feed key information into the airport tower's computer, such as the planes' altitudes, speeds, airline identifications and flight numbers.

Workers were unable to fix a malfunctioning component in the secondary system during the night, he said, and both primary and secondary systems had to be shut down today for the repair job today.