Key workers on the Challenger shuttle project lacked vigilance, discipline and training, space agency investigators concluded after probing an accident last November that damaged a shuttle booster rocket during assembly.

While the damaged booster cited in the report was not used in last Tuesday's flight, according to space agency officials, the possibility of improper booster assembly is reportedly a focus of the NASA inquiry into the explosion that killed Challenger's seven crew members.

The National Aeronautics and Space Administration also said in the report that workers knowingly used defective cranes and followed unsafe, unapproved handling procedures in preparing segments of the booster for assembly in November.

In the 170-page accident report released today, NASA probers warned that the booster assembly work is so complicated and important that "the potential for other mishaps of this nature must be recognized."

A booster is suspected of playing a key role in the Challenger disaster last week when a fiery plume burst through its side, possibly contributing to the explosion.

In another development today, a leading U.S. rocket expert said he had repeatedly asked NASA to study and correct potentially dangerous pressure oscillations -- fluctuations of force against booster walls -- that occur within the giant solid rocket boosters of the shuttle when they are fired.

Professor Gary Flandro of the Georgia Institute of Technology said NASA paid little attention to his studies. He asserted that instead of ordering a full research program, as he had long advocated, NASA installed pressure-oscillation measuring devices on four boosters that powered shuttles into orbit in 1983 and 1984.

No evidence has been presented publicly linking fluctuations to the accident. NASA officials at the Kennedy Space Center here confirmed that instruments to measure pressure oscillation were installed on four boosters. But they could not provide further information on why the agency ordered the measurements, or whether other decisions regarding pressure oscillations had been taken.

Asked for comment today, David L. Winterhalter, acting NASA director for shuttle propulsion, said "I don't know anything about that. I can't say anything about it."

The accident report released today concerned damage to a portion of the left-hand solid rocket booster on Nov. 8 at a Morton Thiokol processing facility. The right-hand booster is suspected of having failed during the first minute of Challenger's flight last Tuesday. The shuttle was destroyed and its crew killed in the nation's worst space accident.

The November mishap occurred as workers prepared to remove one of the heavy steel rocket cross-sections from a railroad car that had brought it from a Utah factory to the Kennedy Space Center here.

According to the report, assemblers improperly lifted the rocket segment with a crane that could not measure the pressure it applied to loads. During the effort, there was a loud "bang," and the massive handling ring around the segment "jumped upwards," the report said.

Probers found "lack of discipline" by workers in following procedures, indifference by quality control supervisors, and a "general attitude of 'I was doing something else at the time,' 'I only look at what I have responsibility for' and 'That's not part of my job.' "

The probers recommended that workers' training records be kept current, that the role of quality control "needs to be defined by management" and proper briefings precede crucial assembly work.

"It should be stressed to the team leader that he is responsible for the discipline of the team and its performance," the report said.

In another NASA report last June, a Lockheed Corp. subsidiary in charge of shuttle maintenance, was accused of a long list of contract violations, Reuter reported today. The violations included misusing heavy equipment, training workers improperly, turning out flawed work and violating safety standards at the hangar where the shuttles are cleaned and repaired, Reuter reported.

Flandro, the rocket expert at Georgia Tech, made his remarks about pressure fluctuations in an interview with The Washington Post. He said he believed the data collected from these instruments NASA attached to four shuttle flights was insufficient to establish the cause or the cure for the oscillations.

"The oscillation question is very significant," asserted Flandro. "It sets up pressures that affect the rocket nozzle thrust, and sets up vibrations that can be severe."

Flandro said he received three $75,000 grants from Morton Thiokol Inc., builders of the boosters, to study oscillation. Calling Flandro "a very good man," Morton Thiokol spokesman Gilbert Moore confirmed the grant, adding, "I personally don't know that he's uncovered anything important, but he obviously feels otherwise."

Another rocket expert familiar with Flandro's work said he is convinced that the oscillation questions are "serious enough that NASA should have continued gathering telemetry," or sensor readings from the rockets.

Dr. Edward Price, also of Georgia Tech, declared: "Pressure oscillations are a recognized problem in the SRB the solid rocket booster . Designers are aware of it. The thing that bothers both of us is that the pressure oscillations are variable and they [NASA] did not monitor it enough to know as much as they should.

"There came a time when they cut back the telemetry to make way for bigger payloads."

Flandro and Price said Flandro's worries, contained in a series of technical and professional papers, were discussed at numerous seminars and conventions of rocket specialists. Flandro, 51, said his position on the potential dangers of such oscillations "has been consistent and is well-known to NASA."

He said the oscillations within the stiff, metal rocket motor could be caused by uneven burning rates of the solid fuel propellants. In turn, he said, the pressure fluctuations are known to have caused variations of up to 100,000 pounds of thrust during an SRB shuttle flight.

"It's like an unbalanced wheel on your car," he said of the effect on the shuttle system.

More important, Flandro said, the pressure fluctuations can set up severe vibrations inside the 149-foot long rocket that add unusual, unpredictable stresses to the casing containing the fuel.

Flandro said the oscillations are increased by the boosters' unusual construction: They are assembled from sections that are stacked and fastened. Most solid fuel rockets are made from a single casing.

The propulsion section of the 1.3 million-pound rockets is constructed of four segments, each containing two segments of propellant.

The burning fuel creates pressures inside the casing of 600 to 700 pounds per square inch (psi). Fluctuations seldom add more than one psi of interior pressure. But the cumulative effect of the eddies in the flame path can alter thrust, Flandro said, as well as cause unwanted vibrations.

Price, 65, a dean of American rocketry, said he remains deeply troubled over the possibility that propellant of Challenger's boosters may have undergone substantial cooling during the cold spell that gripped the launch site in the weekend of delays preceding the ill-fated flight.

NASA has discounted the cold as a factor, but Price remains unconvinced. "The truth is the outer parts of the propellant got colder, and the innner parts didn't. This means expansion and contraction rates are different when the rocket is fired, particularly in the regions of bonds between fuel segments."