An article yesterday on the probe of the Challenger disaster incorrectly reported that National Public Radio had interviewed Allan J. McDonald, an engineer for Morton Thiokol, the company that made the shuttle's solid rocket boosters.

The Morton Thiokol Inc. official who approved the launch of the Challenger over objections of subordinates -- apparently acceding to NASA pressure to get on with an already-delayed liftoff -- said in his written evaluation that cold temperatures could compromise the primary seals on the space shuttle's booster rockets but assured NASA that the backup seals would function.

That assurance the night before the launch, however, contradicted Thiokol's study of August 1985, of which the National Aeronautics and Space Administration was aware, that there was "a high probability" of the backup seals failing if the primary seals were ruptured. It also was at odds with NASA conclusions in February 1983 that the backup seals would probably fail and that corrective measures were needed.

NASA and the maker of the booster rockets had found that pressures inside a firing booster warped the joints enough to prevent the secondary seals from working. NASA, however, continued to fly shuttles while searching for a better way to seal the joints.

Copies of the approval document, signed by Joe C. Kilminster, vice president for Thiokol's space booster programs, were released late yesterday by NASA.

Although the document does not reflect the strong warnings against launching Challenger voiced by several Thiokol engineers, it says "calculations show" that Challenger's O-ring seals "will be 20 degrees colder" than on any previous launch and that they would not be as resilient.

Proper resiliency is essential if the rings are to seat tightly in the gap between booster segments, and on Jan. 28, the day of the launch, temperature readings on the right-hand booster showed it was 7 to 9 degrees, more than 40 degrees colder than the air temperature on any previous launch.

But the document, wired from Thiokol's Utah plant to Cape Canaveral at 11:45 the night before the disastrous launch, took a reassuring tone: "More gas may pass primary O-ring before the primary seal seats. If the primary seal does not seat, the secondary seal will seat."

Films of the Challenger launch show a large puff of black smoke emerging near a joint of the right-hand booster less than a second after the solid rocket fuel was ignited. Because rocket fuel burns with a white smoke, this is thought to have been the result of hot gases burning the O-rings or the putty that is supposed to protect the rings, or both.

Despite the 1983 study and the engineers' warnings, Kilminster concluded that the launch of Challenger "will not be significantly different" from that of the space shuttle Discovery, which was launched the previous January when the temperature was 51 degrees.

NASA's pressure on Thiokol to approve the launch, according to Allan J. McDonald, a Thiokol engineer, came in a series of telephone calls between NASA officials in Florida and at the Marshall Space Flight Center in Huntsville, Ala.

Several times, McDonald said in a National Public Radio broadcast yesterday, NASA officials argued against Thiokol's initial recommendation not to launch. Eventually, Kilminster was persuaded to tell NASA that the data on temperature effects were "not conclusive" and that the launch should proceed.

Meanwhile yesterday, NASA acting administrator William R. Graham named Richard H. Truly, who has flown three shuttle missions, to take over the shuttle program and lead NASA's internal review of the Challenger explosion.

Truly, a rear admiral who previously headed the Naval Space Command, immediately declared his readiness to examine the process that yielded the decision to launch despite warnings from Morton Thiokol and to change that process if necessary to ensure the safety of future shuttle flights.

The presidential commission investigating the accident has said NASA's decision-making process may have been flawed.

"This tragic accident," Truly said, "is going to cause a review -- and if nobody else does it, I will -- to make sure that the organization and the process that NASA has is proper."

Jesse W. Moore, who had held both jobs now given to Truly and who played a key role in deciding to launch Challenger, assumed his duties as director of the Johnson Space Center in Houston, a post to which he was named five days before the disaster.

Although Graham's action complies with the recent request by the commission to remove from the investigating team those who had a hand in deciding to send the shuttle up, Graham insisted the move was not a direct result of the commission's request.

However, according to a NASA statement issued before the launch, Moore was to have stayed as head of the shuttle program until May.

Graham and Moore defended the process used to decide whether it is safe to attempt a launch but conceded something went wrong.

"It's not the policy of NASA to launch the shuttle system on anything less than a hearing of all concerns and all views and all issues associated with the launch," Graham said. "Undoubtedly, something was not right in this launch, perhaps technically, perhaps procedurally. If that process broke down, then it should not have."

Although Moore maintained his assertion that he was unaware of any warnings from Thiokol about the dangers of cold temperatures, he said, "It is the way this program operates that those issues get bubbled up all the way through the line until they are thoroughly discussed by the appropriate people and then resolved in terms of whether or not it is safe to proceed."

Moore refused to speculate on the point at which the temperature warnings stopped "bubbling up."

One place now under scrutiny is the Marshall Space Flight Center at Huntsville, which is responsible for the booster rocket design and production. The commission's probe is trying to determine how far up far up the center's chain of command the warnings of Thiokol engineers were passed, according to commission and agency sources.

"There is a suspicion the smoking gun is at Huntsville," said one NASA official.

A commission source said that in addition to Moore; his deputy, Arnold Aldrich, the manager of National Space Transportation Systems; Robert Sieck, director of shuttle operations at the Kennedy Space Center, and Richard Smith, the director of Kennedy Space Center, were also unaware of the Thiokol protests.

However, sources say the situation is most "fuzzy" at Marshall where at least one senior official, Lawrence Mulloy, manager of the solid-rocket booster program, participated in the meeting with Thiokol executives and successfully urged them to reconsider their opposition to the launch. Mulloy's superior at Marshall, Judson A. Lovingood, the deputy manager of the shuttle projects office at Huntsville, was also at the meeting.

In public testimony before the commission last week, Lovingood mentioned that "there was some concern about the cold temperatures," and then added that Thiokol "recommended to proceed" without telling the panel about the continued objections of company engineers.

One key question facing the panel is who else besides Mulloy and Lovingood were aware of the protests. Lovingood's direct superior is Stanley Reinhartz, manager of the shuttle projects office, who in turn reports to William R. Lucas, the Marshall director.

The story of how Thiokol engineers fought to stop the launch but were overruled was reported yesterday by National Public Radio and other sources.

Thiokol engineers first learned of the subfreezing weather at Cape Canaveral early the day before the launch. NPR quoted one engineer as saying, "We all knew what the implication was. . . . We all knew if the seals failed, the shuttle would blow up."

That evening, several engineers spoke to NASA officials in a conference call. They reminded NASA of the warping problem that could unseat the backup O-rings and that the cold could stiffen the seals.

The engineers said lab studies showed that below 50 degrees, the seals lose much of their ability to hold. It would be 10-to-20 degrees colder at the Cape the next morning. Thiokol told NASA not to launch Challenger.

NPR reported that George Hardy, on the line from the Marshall Space Flight Center in Alabama, said, "I am appalled by your recommendation." NASA's Mulloy argued with the engineers, according to the report, and finally exclaimed, "My God, Thiokol, when do you want me to launch? Next April?"

Thiokol engineers stuck to their guns, and the decision was transferred to company management.

After some discussion, Thiokol General Manager Jerry Mason told NASA his company would approve the launch. Mulloy then told him to sign the document "right away" and send it to NASA officials.

McDonald and other Thiokol engineers, however, continued to dispute the decision, according to senators briefed by McDonald.