MEMPHIS, Tenn. (AP) — Communications equipment failed Tuesday at a regional air-traffic control center, shutting down all airline traffic within 250 miles of Memphis and causing a ripple effect across the country that grounded dozens of passenger and cargo flights.

The problem started when a major telephone line to the Memphis center went out at 12:35 p.m. EST. The Federal Aviation Administration said air-traffic control operations were back to normal about three hours later.

Air-traffic control centers in adjacent regions handled flights that were already in the air when the problem was discovered.

‘‘The airspace was completely cleared by 1:30 (p.m.) Eastern time,’’ FAA spokeswoman Kathleen Bergen said.

High-altitude flights through the region — which includes parts of Alabama, Mississippi, Arkansas, Missouri, Indiana, Kentucky and Tennessee — were discontinued while the equipment was being fixed.

‘‘What we did is put a ground stop in place for any flight that would transition through that airspace. We held them on the ground wherever they were, whether it was Miami, Seattle, Los Angeles, Boston,’’ Bergen said.

The FAA’s action had a ripple effect in several airports. Some airlines experienced delays of up to three hours and were still recovering from the outage Tuesday evening, Air Transport Association spokesman David Castelveter said.

David Magana, a spokesman at Dallas-Fort Worth International Airport, said about 50 flights had been delayed, but were in the process of departing Tuesday afternoon. About 50 other flights had to be canceled.

In Nashville, 12 Northwest Airlines flights were diverted, and 25 to 30 departures had been delayed one to two hours, airport spokeswoman Emily Richard said. Disruptions affecting fewer flights were reported at airports in Los Angeles, St. Louis, Miami, Pittsburgh, Louisville, Ky., Kansas City, Mo., Tampa, Fla., and Charlotte, N.C.

Nancy Castles, a spokeswoman for Los Angeles International Airport, said at least eight flights were delayed. ‘‘That’s not too bad at all; it’s probably not even noticeable,’’ she said.

Vernon and Dorothy Thompson, who live in southwestern Kentucky, were delayed at the Nashville airport before flying to New Zealand. ‘‘This is not the way to start out our dream vacation of a lifetime,’’ said Vernon Thompson, 64.

Bob Erickson, a traveling Fruit of the Loom underwear salesman from Bowling Green, Ky., said he was delayed five hours in Nashville on his way to New York. ‘‘What are you going to do?’’ a stoic Erickson said. ‘‘There’s absolutely nothing you can do.’’

No major problems were reported at Atlanta’s Hartsfield-Jackson Airport or Chicago’s O’Hare and Midway airports, aviation officials said.

Memphis, with the headquarters of shipping giant FedEx Corp., is the world’s busiest airport for cargo, handling 4.08 million tons of air freight in 2006. The Memphis airport also is a hub for Northwest Airlines.

FedEx Express had to divert only 11 incoming flights which caused no major disruption in its delivery schedules, company spokeswoman Sandra Munoz said. The busiest part of the company’s day is early in the morning.

Operations were back to normal by about 3:30 p.m. EDT, said Laura Brown, a spokeswoman for the FAA in Washington.

Brown said the outage affected the center’s ability to talk to flights passing through its airspace and to other air traffic control facilities.

Brown had no further details, including which telephone company operates the line that was lost. She would not comment on a statement from the Air Traffic Controllers union that was e-mailed to reporters, explaining that its members had to use personal cell phones to talk to other facilities about specific flights immediately after the Memphis center lost communications.

The Memphis center is one of 20 around the country. It handled almost 3 million flights last year, ranking it ninth among the 20. ‘‘It’s a big airspace, and there are lots of airplanes,’’ Bergen said.

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AP Business Writer Dan Caterinicchia in Washington and AP Writer Travis Loller in Nashville contributed to this report.