Federal investigators seeking the cause of the dramatic barrel roll and sudden 29,000-foot descent of a TWA jetliner carrying 86 people near Detroit Wednesday night discovered yesterday that the tape that is supposed to record air crew conversations is blank.

The plane, on a scheduled nonstop flight from New York to Minneapolis, made an emergency landing in Detroit. Three people suffered minor injuries.

The blank tape added to the mystery of what happened to TWA Flight 841, a Boeing three-engine 727 and one of the most reliable airplanes ever built. The consensus of investigators interviewed yesterday was that they were looking for some type of unspecified control failure, possibly involving the automatic pilot.

"We've never had anything like this before," Boeing spokesman George Weiss said. Boeing engineers have joined the investigation under the direction of the National Transportation Safety Board.

One of the key tools in any accident investigation is the cockpit voice recording, which is supposed to be sealed in a crash-proof box and contain the most recent 30 minutes of conversation on any flight.

"There's simply nothing on (the tape) until the last couple of minutes after they were safely on the ground," a knowledgeable aviation source said. TWA spokesman John Corris confirmed the report, stating that "the information we have is that we do not have a usable tape."

According to the Federal Aviation Administration, the cockpit voice recording, when it is working properly, can be erased by a switch in the cockpit only after the plane is on the ground and the brakes are locked.It could not be determined yesterday why the tape was blank.

Investigators agreed yesterday that "barrel roll" was probably the best way to describe what the plane did, based on interview with the crew.

In a barrel roll according to the FAA's Curt McKay, a plane rolls to one side while maintaining its forward movement and then continues rolling until it returns to its original position. A complete barrell roll would be a 360-degree rotation of the air-craft.

"If you do a good barrel roll," McKay said, "you can put a cup of coffee on the floor and not spill a drop." The centrifugal force of the roll apparently kept many persons in the 727 from being hurled about, investigators said.

In the passenger cabin, there were moments of horror. "You could feel your face pressed back and the blood rush to your head," 22-year-old Chell Roberts, aUniversity of Utah student, told the Associated Press. "Everyone was screaming. I thought it was over . . . It's really a funny feeling to see what everybody does before they think they are going to die."

The incident began about 10 p.m. when the plane was cruising at 39,000 feet, 2,000 below its maximum rated altitude. According to federal investigators, Capt. Harvey Gibson noticed that the autopilot was making hard corrections to the left in the plane's course as the plane began to roll to the right. Gibson disengaged the autopilot and took manual control.

The nose dropped precipitously, perhaps to a 60-degree angle, and the plane picked up speed as it plummeted toward the ground. The aircraft may have exceeded the speed of sound, about 625 miles per hour.

The pilot cut power to the engines, and extended the "spoilers" flaps on the topside of the wing, to increase drag and slow the plane.

The jet continued to spiral downward. Then Gibson extended the landing gear to further and increase drag. Only then was he able to regain control. In a matter of minutes, the plane had dropped to about 10,000 feet.

Gibson requested and emergency landing in Detroit, and it was described as smooth but hard. He had trouble overcoming the plane's tendency to turn to the left as the plane was landing.

Boeing 727s are not designed to do barrel rolls and break the speed of sound. The fact that this one did, and survived, means that the airframe "is as strong as brick," as FAA Chief Langhorne Bond put it.

The spoilers and wing flaps were broken or ripped off during the incident and there was damage to the landing gear door believed to have occurred when the gear was extended while the plane was at top speed.

Investigators hope they can learn exactly what the plane did from the flight data recorder, a device that records flight control actions and many other mechanical functions. The flight data recorder is in good shape, safely board officials said yesterday.

The jet involved was a Boeing 727-100, an early model of the aircraft. It was delivered to TWA in July 1965. Boeing has sold 1,446 727s, with 1,031 of them going to domestic carriers. That is almost half of the domestic commercial fleet.

The incident occurred in clear weather, and investigators said they did not believe unexpected clear-air turbulence was a factor, although nothing can be ruled out this early in such an investigation.

No other planes were within miles of the TWA flight, according to an FAA spokesman.

The cockpit voice recorder was first required on commercial airliners in the early 1960s over the objections of the Air Line Pilots Association (ALPA), which represents most pilots, and the Air Transport Association, which represents most airlines. ALPA has consistently opposed "premature" release of the transcript of the conversations of crew members, saying that such conversations could only be understood if taken as part of the full investigative record of the flight. CAPTION: Picture, FAA Chief Langhorne Bond inspects damaged underside of 727 that went out of control but was landed safely. AP