The presidential commission on the Challenger disaster yesterday disclosed that "at least three key NASA officials" were not informed before the Jan. 28 liftoff of strong objections to launching made the night before by officials at Morton Thiokol Inc., who were concerned about the effect of the unusually cold weather on the shuttle's solid rocket boosters.

Some company engineers were so concerned, even after booster manufacturer Thiokol signed a statement for the National Aeronautics and Space Administration "indicating approval of the launch," that a number of them "still strongly urged" against it, according to the commission statement.

Among those objecting was Allan McDonald, director of Thiokol's solid rocket booster or SRB project, sources said. A witness to the prelaunch discussions told The Washington Post yesterday that McDonald argued that "it's so damn cold and none of us are really sure of anything . . . . "

The three NASA officials, who sources said were directly involved in deciding whether to launch, "had not been notified and did not know" of these objections, the commission statement said.

The commission is now focusing on who knew what and when they knew it, a source close to the investigation said last night. That information, and all data concerning the cold, is considered crucial. The leading theory on the cause of the accident is that the unprecedented low temperatures before launch may have decreased the effectiveness of O-ring seals designed to prevent leakage of hot exhaust gases from the booster rocket. Such a leak in the right SRB is thought to have been the first in a rapid series of events that led to the explosion of the Challenger and the death of its seven crew members about 73 seconds after launch.

It was the impact of the cold on the O-rings that concerned Thiokol engineers during consultations with NASA officials the afternoon and night of Jan. 27, in part because they had noticed damage to the O-rings after previous launches, when temperatures went only as low as the 50s. The temperatures on Jan. 27 and 28 were in the 20s and 30s.

McDonald vigorously opposed approving the mission during a lengthy teleconference with NASA officials, according to company and commission sources. Starting at 5 p.m. Jan. 27, he argued against launch because of concerns about the cold weather.

At the insistence of NASA officials, however, Joe C. Kilminster, a Thiokol vice president, reversed the company's position about 11:30 p.m. and signed a formal written recommendation to go ahead with the launch, company and commission officials said.

McDonald "refused to sign off" and continued making his arguments, they said. McDonald's argument to NASA officials at the Kennedy Space Center in Florida that night was that "it's so damn cold and none of us are really sure of anything . . . we're extrapolating data here," according to Jack Buchanan, manager of Thiokol's Kennedy Space Center operations, who attended portions of the meeting.

"Basically, he was saying, 'Why do we need to go ahead? If we don't know for sure, why should we launch?' " Buchanan said in an interview yesterday.

"In a sense, he was overruled by his own management," he added. "Nobody knew we were going to be in this mess, that it was going to be a disaster."

McDonald could not be reached for comment yesterday. But according to a commission source, McDonald's testimony about his objections to the launch, given at a closed session at Cape Canaveral last Friday, "shocked" panel members.

"We threw everybody out of the room and . . . decided we had to tell the president," said one panel member. "It changed the whole tone of the investigation."

A Thiokol spokesman confirmed yesterday that the company had initially recommended against approving the launch and then switched its position later in the evening.

"We did say we were not in agreement unless it took place in a temperature we had an experience with, which was 53 degrees," said spokesman Tom Russell. "Certainly our [initial] decision was based on the temperature."

The temperature at launch time for Challenger was 38 degrees Fahrenheit, far colder than the previously coldest launch.

Russell confirmed that Thiokol "reevaluated" its position at the urging of NASA. "We looked at the data again and it was the decision of the group with the information that we should change our mind," said Russell.

Russell also said company officials were never informed of unusally cold temperature readings of 7 and 9 degrees recorded by a NASA ice team on the surface of the right SRB.

As described yesterday by Buchanan, the crucial weather debate meeting took place at a large conference room at Cape Canaveral with teleconference hookups to Thiokol offices in Brigham City, Utah, and NASA's Marshall Space Flight Center in Huntsville, Ala. Lawrence B. Mulloy, the head of NASA's solid fuel booster rocket project, was the chief agency official in the room and the most vocal proponent of proceeding with the launch, Buchanan said.

McDonald repeatedly expressed concerns about the impact of the cold weather on the SRBs, including the rubbery seals that bind its segments, as well as the effect the weather could have on rocket recovery teams, Buchanan said.

But Mulloy and other NASA officials urged that the data be "rechecked," he said. After hours of debate, "they [the NASA officials] finally said, 'We want a formal written recommendation' " to launch, Buchanan said.

At that point, Thiokol officials in Utah adjourned for 30 to 40 minutes to meet and then telecopied to NASA a statement signed by Kilminster approving the launch.

"There was no shouting or screaming or anything," said Buchanan. "These are all people who have known each other for years."

Reached at Marshall Space Flight Center yesterday, Kilminster said he would have no comment on accounts of the meeting.

One commission source said that during last week's closed-door hearing on the conflicting Thiokol recommendations, Kilminster was "mute," offering no explanation for why he reversed his position.

An official at Marshall said yesterday that Mulloy was not taking calls from reporters.

A source familiar with the probe indicated that the three NASA officials took direct part in deciding whether to launch Challenger. The source declined to identify the officials, but Jesse W. Moore, NASA associate administrator for space flight, is presumed to be one of them.

The commission, headed by former secretary of state William P. Rogers, is focusing on discrepancies in the various versions offered by NASA officials since the disaster of how the crucial decision to launch was made, as well as what went wrong after liftoff, sources said.

After meeting at the Washington office of Rogers' law firm yesterday, the commission agreed to split up and fan out across the country. Groups of panel members will fly to Marshall in Alabama, Thiokol offices in Utah and Cape Canaveral on Thursday, a commission source said.

Thiokol and NASA engineers for more than three years had expressed serious concerns over the integrity of the joints of the reusable boosters. Inspections after several earlier shuttle flights showed that hot exhaust gases sometimes penetrated the joints, eroding the O-ring seals and threatening catastrophic failure. NASA was seeking a solution, but continued launches at an accelerating pace.

The commission's statement yesterday about Thiokol objections is at sharp variance with the post-launch assurances to the public by senior NASA officials that everyone had agreed to the launch after careful consideration of all the issues, including the weather.

The commission source declined yesterday to say why the newest statement was issued. But on Tuesday, members of a Senate NASA oversight committee sharply questioned Rogers on whether the commission can probe deeply enough to determine the truth of the shuttle's destruction.

The statement said the commission asked at the close of Friday's executive session that Thiokol and NASA collect and deliver to it "any and all documents, memoranda, or personal notes" of any launch decision participant "by the close of business Friday."

The request adds another note of gravity to the panel's activities. In previous NASA mishaps, the agency has directed its own inquiries. But the commission has barred any of NASA's Challenger launch decision-makers from participating actively in the probe.

Meanwhile, Richard C. Cook, the budget analyst who last July warned NASA superiors of possible "catastrophic" failure of the O-rings, has suggested that the tight schedule for Challenger flights in 1986 may bear on the disaster.

In a letter to Rogers, Cook said he attended meetings at which Kennedy launch representatives "made it clear . . . it was essential for Challenger" to be "launched on or near" schedule to ensure enough time to prepare it for a later orbital mission to launch an interplanetary spacecraft that has a launch "window" only once every 13 months. NASA documents he provided with his letter confirmed the concern about scheduling.

Meanwhile, parts of Challenger's right SRB were positively identified 43 miles offshore and one piece was retrieved from the ocean floor, officials said.