The governors of Pennsylvania and Ohio asked over the weekend for federal aid in the wake of the nation's worst tornado disaster in more than a decade.

Pennsylvania Gov. Richard L. Thornburgh (R) requested initial federal assistance of $2 million, but his spokesman, Terry Williamson, said more aid will be needed.

Ohio Gov. Richard F. Celeste (D) declared five counties disaster areas.

"We are hoping for a swift federal disaster declaration for the Ohio area hit by Friday's storms," Celeste said through a spokesman.

In Washington, however, spokesman Bob Blair of the Federal Emergency Management Agency (FEMA) reported late yesterday afternoon that Ohio had not formally filed for disaster relief.

Tracy Knippenburg of the Ohio Disaster Services Agency said the governor would file for federal relief yesterday evening or this morning.

The torrent of twisters that swept across parts of the two states, as well as western New York and Ontario, Canada, Friday evening left at least 91 dead, with more than 800 injured and thousands more homeless, authorities reported yesterday.

Rescue workers, including more than 1,200 National Guardsmen and Canadian troops, sifted through debris in search of more dead or wounded, while survivors returned to the remains of their homes.

The National Guard was also called in to protect devastated areas after more than 50 cases of looting were reported Friday in Trumball County, in northeastern Ohio.

Meanwhile, federal and state officials began trying to determine the cost and extent of the tornado damage.

Pennsylvania, the hardest-hit state, reported 61 persons dead and more than 600 injured. The Pennsylvania Emergency Management Agency also reported that 1,520 buildings had been damaged or destroyed.

Blair of FEMA said that 290 houses, apartments and businesses in Ohio were destroyed and 72 others badly damaged. About 70 percent of the structures were insured, he said.

Sixteen people were reported dead and more than 200 injured in Ohio.

The tornadoes were spawned by a huge storm system that spread from central Ontario south over western Pennsylvania, northeastern Ohio and southwestern New York state.

Meteorologist Paul Fike at the National Weather Service's Severe Storms Forecast Center in Kansas City, Mo., said yesterday that several of the 27 reported twisters had unusually long paths on the ground.

"One touched down near Beaver, Pa., and went for 60 miles on the ground, lifting up at Indiana, Pa.," he said. Another followed a 55-mile path, while a third traveled 25 miles.

Fike said the average tornado stays on the ground for nine miles and a "violent" one may go 26 miles.

At least 14 Canadians, including four children, were reported killed by the tornadoes.

Fike said the disaster was the worst tornado storm since April 1974, when 315 people were killed by twisters that swept through 11 states, causing damage totaling more than $600 million.