An American Airlines jumbo jet carrying 270 people crashed on takeoff from O'Hare International Airport here today after one of its three engines separated from the left wing. There were no survivors, American Airlines and police officials said.

The engine separated from the wing of the DC10 about the time flight 191's nose wheel was lifting off the ground, according to aviation sources in Washington. The plane then rose to about 500 feet, went into a slight left turn, plunged to the ground and exploded.

John Wayne, a passenger in an Ozark Airlines plane that was approaching O'Hare at the time of the accident, said the planed exploded "in a giant red ball."

The plane hit the ground in an open field about one-quarter mile off the end of runway 32 Right, not far from the Oasis Mobile Home Park. There apparently were no deaths on the ground, but three minor injuries were reported.

Robert Anderson, driving nearby, told the Associated Press he "looked up and I could plainly see the plane was banking.

"It was almost vertical, and I almost started to scream because I knew it would not come out of it. I continued almost upside down. . . . When I looked back, it looked like an atomic bomb explosion."

A witness who was standing about 400 feet away from the crash told investigators that the fireball rose so high that he could not see its top. American Airlines spokesman Jim McAllister said the plane carried about 450,000 pounds of jet fuel, about 72,600 gallons.

"It just came straight down." said Terry Sullivan, an assistant Cook County state's attorney, who witnessed the crash from his car on the Northwest Tollway. "Nobody had a chance to get out of it. I couldn't tell that it was missing an engine. It just started gyrations and it went straight down."

The death toll makes this the worst aviation disaster in U.S. history. The previous high toll was 144 deaths last September when a small plane and a Pacific Southwest Airlines Boeing 727 jetline collided over San Diego.

Neil Callahan, A spokesman for the Federal Aviation Administration said he had listened to a recording of the control tower's conversation with the American Airlines plane. Everything was normal to a point, but then the pilot said, "We are rolling."

As the plane's nose wheel lifted off the ground, the controller said to the pilot, "Do you want to come back?"

There was no answer.

The plane, built by McDonnell Douglas, was a wide-bodied jumbo jet that has one engine under each wing and a third engine in the tail. Early reports from the scene put the death toll as high as 279 people, but American Airlines and National Transportation Safety Board officials here said the plane carried 255 passengers and a crew of 15, including 10 flight attendants.

In early but incomplete lists, three of the victims were listed as being from the Washington area. A majority of the passengers and crewmembers were from the Los Angeles area and other southern California cities.

Flight 191 originated in Chicago and was headed nonstop for Los Angeles. Some of the passengers were reportedly going to an American Booksellers Association convention in Los Angeles, but that could not be confirmed.

At Los Angeles International Airport, where Flight 191 would have landed, a few weeping relative and friends gathered at the American Airlines information desk. Some reservation clerks also wept.

Playboy magazine in Chicago announced that four of the victims were its employes, including managing editor Sheldon Wax and his wife, Judith Wax, a well-known Chicago writer. The other Playboy employes were identifed as Mary T. Sheridan and Victoria C. Haiden.

The No. 1 engine, the one under the left wing, was found about 8,000 feet down the 10,003-foot runway, Washington sources said. It could not be determined why it had separated from the wing.

The FAA's Callahan said that the engine "appeared to be relatively intact," indicating that there was no explosion in the engine.

Asked by reporters if the plane should have been able to fly with one engine missing, Callahan replied: "Yes, it should fly, no question about that, but that's one thing that will be determined in a future investigation."

American Airlines and McDonnell Douglas were sending experts to the scene to help in the investigation. The cockpit voice recorder and flight data recorder - the two so-called black boxes - were recovered intact and turned over to the National Transportation Safety Board, officials said.

Michael Lockman, a photographer who sold pictures of the crash to the Chicago paper, said that after the engine blew off, there was "dense smoke. The flight was then level for a minute, then banked sharply to the left and hit the ground at about a 90-degree angle."

FAA officials in Washington said witnesses had estimated various angles, but all agreed that the plane disintegrated as it struck.

Skies were clear at the time of the accident, but there was a 30-mile-an-hour north wind.

O'Hare, which was packed with Memorial Day weekend travelers, was closed briefly. Some runways were reopened later, but departing flights were delayed an hour or more.

The federal Bureau of Investigation entered the post-crash probe, as it routinely does. John Otto, special agent in charge of the Chicago field office, said "there is no indication of intentional sabotage."

Hospitals were alerted immediately after the crash, which occured at 3:02 p.m. local time. The alert was canceled later. Ambulances ringed Elk Grove Road on the north side of the airport and roadblocks were set up to keep sightseers away.

Chicago Mayor Jane Byrne was one of the first public officials on the scene. She called the crash "probably the worst thing I've ever seen."

Rescue workers walked throught the smoking rubble, marking bodies with 4-foot-high metal stakes topped by red, yellow and black flags numbered to indicate how many bodies lay beside the stakes. A temporary morgue was set up in an American Airlines building.

"Underneath the left wing was on fire. Stuff was coming out like white vapor." John Zucarro, who saw the crash from the ground, told the Associated Press.

"One of my superintendents just came back from the field and he said, 'There's bodies scattered all over.'"

The plane was piloted by Capt. Walter H. Lux, American Airlines officials said. The first officer was James R. Dillard and the flight engineer was Alfred F. Udovich. The two ectra crewmembers in the cockpit were not immediately identifed, but it is common for airline employes to "dead-head" in cockpit seats. CAPTION: Picture 1, Firemen, searching through wreckage of American Airlines jumbo jet near O'Hare International Airport, work around part of the landing gear, one of the largest remaining pieces of plane. UPI; Picture 2, Metal stakes rise above jetliner's wreckage, their numbers indicating the number of bodies that lie nearby. No one aboard flight 191 survived the crash. AP; Picture 3, An engine rests amid the wreckage of DC10 that crashed on takeoff yesterday at O'Hare and exploded into a "great red ball." On of its three engines felloff as the plane was ascending. UPI