A plan by the Boeing Co. to reduce the number of emergency exits in its 747 jumbo jets was thwarted yesterday when the Federal Aviation Administration announced it will require 10 exits instead of eight as the manufacturer proposed.

FAA chief T. Allan McArtor announced the decision at the start of a House Public Works subcommittee hearing where two flight attendants who survived 747 accidents were waiting to describe difficulties in evacuating the jets.

"Prudence," McArtor said of his decision during a break in the hearing.

FAA rules require two exit doors for every 110 seats and that a manufacturer be able to show that a fully loaded aircraft can be evacuated in the dark within 90 seconds, with half the doors inoperable. Most 747s operated by U.S. carriers seat from 350 to 440 passengers.

But the new rule, which McArtor said should be final by late summer, will also require passengers to be seated not more than 30 feet from an exit door, and that adjacent doors be separated by not more than 60 feet. In the case of the 747, that would require five pairs of exit doors on the main passenger deck.

Boeing had proposed eliminating an over-wing exit door on each side of the plane, which would put 72 feet between exits.

In his testimony, McArtor said he had seen persuasive arguments for 70 feet between exits as well as 60 feet, and emphasized that the distance between doors is not the only safety factor to be considered.

But Joan Jackson, a flight attendant who survived the worst aviation accident in history, countered that distance is critical in evacuations. Jackson was aboard a Pan American World Airways 747 taxiing on a runway in the Canary Islands when it was hit broadside by a KLM 747 attempting to take off. The 1977 accident killed 583 people.

"Could you move 70 feet in 90 seconds?" she asked. "What if the plane is dark and filled with smoke? What if you are climbing over luggage? What if you are trying to carry your small child?"

Orvil M. Roetman, Boeing vice president of internal affairs, said the manufacturer disagrees with the FAA's decision. "We think 70 feet is defendable and we think our analysis supports that," he said.

He said any change in configuration of the doors would have little financial impact on Boeing, but added individual airlines have estimated the financial impact to be between $700,000 and $2.3 million per aircraft per year, primarily because of additional seats that could be installed in the cabin.

He said 100 of the jumbo jets are operating today with an eight-door configuration. Those jets are operated by foreign carriers.

The debate over exit doors dates to 1983 when Boeing asked for FAA permission to eliminate its over-wing exits. The agency's Seattle-based aircraft certification office approved the request, but when word reached FAA headquarters here, then-FAA chief Donald D. Engen balked.

Last July, the FAA advised Boeing that it would not certify the new 747-400 model without the over-wing exits, and in October, the agency announced it was writing a new rule regarding the distance between exits.

In the meantime, McArtor, who took over the FAA in late summer, said he wanted to reexamine all the arguments. A January speech McArtor made at the Boeing factory in Seattle signaled to flight attendants that he was edging toward the manufacturer's point of view.

But to reverse the FAA's earlier position, McArtor would have faced stiff and vocal opposition from Congress, which framed the issue as a choice between safety and dollars.

"Never should we allow human safety to be sacrificed on the alter of economics," Rep. James L. Oberstar (D-Minn.) reminded McArtor at the hearing.

Oberstar, who chairs the investigation subcommittee, said he called yesterday's hearing after rumors reached him that McArtor was inclined to go with Boeing's proposal.

"I was concerned that insider contacts we have indicated they {the FAA} may be leaning in the direction the industry wants them to lean and Boeing wants them to lean," Oberstar said in a recent interview.

McArtor acknowledged after testifying yesterday that "there were lots of rumors. They were created by people understanding that I was looking into the issue in great depth because I had reopened the issue."