WASHINGTON -- A cascading computer failure in the nation's air-traffic control system caused severe flight delays and some cancellations along the East Coast Friday.

A computer system in Atlanta that processes pilots' flights plans and sends them to air-traffic controllers failed late Thursday or early Friday, Federal Aviation Administration spokeswoman Diane Spitaliere said.

In response, the agency rerouted the system's functions to another computer in Salt Lake City, which overloaded because of the increased volume of data, magnifying the problem.

The FAA could not immediately calculate the number of flight delays caused by the problem, which was made worse by bad weather, Spitaliere said.

Although the computer problem was fixed shortly before 11 a.m. Friday, its impact lingered on into the late afternoon, especially in New York, where computer systems took two extra hours to get back online, Spitaliere said.

Doug Church, a spokesman for the National Air Traffic Controllers Association, said the problem forced controllers to enter flight information manually, which he described as a time-consuming practice.

"With some of these East Coast airports, nothing is getting in right now," Church said Friday afternoon.

AMR Corp.'s American Airlines spokesman Tim Wagner said the nation's largest carrier experienced about 50 cancellations on the East Coast, with LaGuardia departures being hit the hardest.

Hundreds of flights were delayed for two to three hours at LaGuardia, John F. Kennedy International and Newark Liberty International Airports, said Steve Coleman, spokesman for the Port Authority of New York and New Jersey.

Linda Rutherford, a spokeswoman for Southwest Airlines Co. said the airline experienced delays on about 40 percent of its 3,300 daily flights -- the majority because of the air-traffice control problems.

Betsy Talton, a spokeswoman for Delta Air Lines Inc., said the Atlanta-based airline was experiencing delays of roughly two hours Friday in the Northeast, but she attributed the backlog to thunderstorms.

Flight delays in the rest of the country were not as severe, Spitaliere said.

Earlier this year, the FAA highlighted an expanded air traffic control strategy intended to minimize weather-related delays this summer. The agency's "airspace flow program" is designed to allows airlines to choose between flying longer routes to avoid stormy weather or accepting delays that are aggravating for fliers and costly for the industry.---- FAA officials said the program would allow airlines to choose between taking a delay or flying around the storm.