A small Allegheny Airlines plane carrying 21 passengers from Washington National Airport to Philadelphia was forced to dive yesterday afternoon to avoid hitting a plane dropping skydivers, Federal Aviation Administration and Allegheny officials confirmed.

"We had nine free-falling bodies in front of us," the captain told the passengers immediately after the incident, according to passenger, Richard L. Homan, a Washington Post editor. No one was reported injured.

"It was one of those things where your stomach is suddenly up in your neck," Homan said.

The pilot, identified by Allegheny as James Gianotti, told both the passengers and Allegheny officials that he had received no warning of other airplanes from the FAA's air traffic controllers.

Skydivers and their pilots are required by federal air regulations to notify the air traffic control service when and where they plan such activity. Such drops are prohibited in active airways.

When dives are planned, that fact is supposed to be published in a "notice to airmen," which pilots are expected to check. "Whether any of this was done or not, I can't tell you," FAA spokesman Dennis Feldman said.

Both airline and general aviation pilots have complained in the past about unannounced skydiving operations.

Allegheny Flight 564 was a twin prop-jet M298 and carried a crew of three. It left Washington National at 1:04 p.m. The incident occured about 30 minutes later near Wilmington.

According to Allegheny spokesman Dave Shipley, the pilot had just received instructions to descend from 9,000 feet to 7,000 feet when the incident occurred.

Homan said that the Allegheny plane dived sharply to the left, then dived again after the drop plane made another maneuver that put the planes back on a collision course. The drop plane did not appear to be in radio contact with anybody, Homan said the Allegheny pilot told the passengers.

"We have not gotten into any real detail yet," Allegheny's Shipley said. "We will file a near-miss report with the FFA."