Almost two of every three Americans assign at least "a fair amount" of blame for the Challenger shuttle disaster to NASA officials, according to a new nationwide Washington Post poll. At the same time, the poll shows, a large majority, three of every four, trust the space agency now to run a space program that "is as safe as it should be."

The poll comes as the president's commission investigating the disaster opens two days of hearings today by calling as witnesses some of the key officials who opposed each other during conferences the night before the Challenger's Jan. 28 liftoff and explosion.

Lawrence Mulloy, the space agency manager who is said to have advocated the launch despite doubts among engineers of the firm that made the shuttle's solid-rocket boosters, is likely to draw the most interest at the session. Mulloy is one of three officials of the National Aeronautics and Space Administration the commission has asked to testify.

Allan McDonald, who has emerged as the most outspoken of the booster-maker's engineers who opposed the launch, is one of five employes of Morton Thiokol Inc. called to testify. McDonald has given vivid accounts to journalists of conferences between NASA and Thiokol the night before liftoff.

He has depicted Mulloy as urging approval despite opposition by Thiokol engineers who were worried that subfreezing weather at the launch pad would impair the performance of rubber O-rings that seal the booster's four main segments.

Mulloy, manager of the booster program for the space agency's Marshall Space Flight Center at Huntsville, Ala., has declined to comment.

In the poll, in which 1,008 people were interviewed by telephone on Sunday, 31 percent said they assign "a great deal" of the blame for the explosion to NASA officials and another 31 percent said NASA officials deserve "a fair amount" of the blame. Twenty-four percent gave NASA little or none of the blame, and 14 percent offered no opinion.

The survey showed a slight decline in support for the shuttle program in recent weeks, with 74 percent saying it should continue despite the blast that took the lives of seven crew members. In a Post-ABC News survey in mid-month, 83 percent said the program should continue.

In the new poll, 35 percent said they have a great deal of trust in NASA to run a safe space program now, and 42 percent said they had a fair amount of confidence. Eighteen percent said they had either "not much" or no confidence in NASA, and 5 percent expressed no opinion.

The other NASA officials include Roger Boisjoly, head of a special task force studying the problems with the seals, which first emergedthree years ago, and Arnie Thompson, supervisor of structures at Marshall.

Neither NASA nor the commission has issued any findings, but the right booster is suspected of a malfunction caused when unusual cold stiffened the O-rings of one joint, preventing them from sealing properly, which allowed blowtorch-like exhaust to escape through the side of the rocket casing, setting off the volatile fuel in the shuttle's huge external tank.