The speakers at the pep rally for "Star Wars" were preaching to the choir.

The 186 contractors who went to the Cannon Caucus Room for a day of superfluous reinforcement of their endorsement of the president's Strategic Defense Initiative agree with him entirely that it will "render nuclear weapons impotent and obsolete."

Outside the room, doubts are on the rise. Will the nuclear-powered, computer-driven contraption protect our people, as President Reagan first said, or will it be a shield for our missile sites? The president's admission that it cannot be 100 percent leakproof left skeptics wondering if it would be their city that would be out in the rain when a hole appeared in the "umbrella."

And more importantly, in the wake of the president's final annulment of the SALT II treaty, the question arises whether SDI is the alpha and omega of Reagan's arms control philosophy.

The presence on the podium of Ambassador Edward L. Rowny suggested as much. Like the others, he got a plaque from the sponsors, the privately funded U.S. Space Foundation, saying "Thank you for your support." At any other gathering, someone might have asked how come the president's special adviser on arms control was promoting a system that is regarded as one of the principal obstacles to an agreement with the Soviets.

In the question period, Rowny artlessly and perhaps inadvertently suggested, that despite a mildly conciliatory and patronizing presidential speech in Glassboro, N.J., Reagan's ideas about arms control have not changed since he took office, or in fact since he began his political career.

For instance, Rowny cheerfully referred to "tremendous structural problems within the Soviet economy" that Gorbachev "minimizes."

He seemed to be hinting at the old Reagan theory that we can bankrupt the Soviets. Spending for Star Wars is estimated at trillion. If the Soviets try to match it, they will be paupers and no longer a threat.

When Rowny was asked by a questioner about the "joint ventures in space," between the superpowers, a possibility the president once airily mentioned, Rowny brought him quickly down to earth.

"What he was talking about was approaching these regional issues like Afghanistan, Ethiopia, Kampuchea, looking at bilateral problems."

In other words, arms control isn't everything. It may be attainable if the Soviets behave themselves and put Reagan in the proper frame of mind.

The president has been much put out at the uproar occasioned by his abandonment of SALT II. His Glassboro speech, however, sounded more like the utterance of a man who wants a summit meeting with a Soviet leader -- a most palatable political exercise, and a sedative for restless voters -- more than he wants an agreement with the Soviets, the inveterate violators of arms pacts.

The resistance to Star Wars has surfaced, surprisingly, in the Senate, where 48 members have signed a letter complaining that they really don't know what it's all about. The defense establishment was considerably rattled by the fact that J. Bennett Johnston of Louisiana (D) and Sam Nunn of Georgia (D) were among the naysayers -- "they are considered reliable by the community" said one Star Wars fan at the meeting. They are joined by liberals who think that the ABM Treaty will be the next pact sent to the dustbin of history.

Defense Secretary Caspar W. Weinberger followed Rowny on the program. He mentioned the critics, but did not answer them.

He wearily pointed out the irony of having SALT II elevated and Star Wars put down.

"The hopeful is spurned and the flawed is embraced," he said.

"If we can destroy Soviet missiles before they get into the earth's atmosphere, as we seek to," he said, "we will be able to protect our people; and if we can do that, we will make the missiles obsolete and impotent."

The "ifs" bother many, especially 1,600 scientists, including some who work at laboratories at Lawrence Livermore and Los Alamos, which are deeply engaged in SDI research. They sent a letter to Congress urging a slowdown in spending. Both houses seem inclined to take that advice. They don't think the trillion-dollar scheme will work. It won't save cities and if it just protects missile sites, it finishes ABM.

Edward Teller, father of the H-bomb, and originator of Star Wars, dismissed the dissident scientists, "I wonder if there is any statement for which you couldn't get 1,600 signers from that type of people. In science we would call that a fluctuation, and a fluctuation is not the wave of the future."

That's less certain now.