The same day that President Reagan gave his "Star Wars" speech last week, the Pentagon official at the heart of the effort told Congress he "would not recommend" spending more money than already budgeted to study ways to stop missiles with beams of light shot from space.

Another Pentagon space research executive estimated at the same Senate Armed Services subcommittee hearing that the High Frontier space-based missile defense advocated by retired Army Lt. Gen. Daniel O. Graham, formerly head of the Defense Intelligence Agency, would cost "$50 billion to $75 billion or more."

The Pentagon testimony before the Senate strategic and theater nuclear forces subcommittee indicates that Reagan caught many Pentagon professionals by surprise when he called for an intensified effort to perfect a missile defense.

Otherwise, it is unlikely that the Pentagon's expert witness on the destructive beams of light known as lasers would have cautioned against speeding up the current program, as he did in this exchange with Sen. Dan Quayle (R-Ind.) on March 23, the same day Reagan sounded his call for greater effort:

"Can you recommend to the committee an acceleration of the space-based laser technology program on technical grounds?" Quayle asked.

"Senator, no, I cannot at this point in time," replied Air Force Maj. Gen. Donald L. Lamberson, coordinator of the Pentagon's directed-energy weapons program, including lasers.

"A great amount of thought went into the plan which was submitted by the secretary of defense last year, and which is the plan for space-based lasers that we are working against," Lamberson continued. "We believe that it is a balanced plan which vigorously attacks the technology that needs to be revealed.

"In balance with other programs of the Defense Department, we stand behind that plan and would not recommend an acceleration at this point."

Lamberson said that by sticking to the present laser research program, the Pentagon should, after spending "just under $1 billion," know by 1988 where to go next in space-based lasers. To proceed beyond that research to "any kind of operational capability would obviously be many times that cost," he said.

Graham's High Frontier concept calls for stationing in space satellites armed with non-nuclear weapons to knock down enemy missiles. The backup for these space defenses would be rapid-firing guns or non-nuclear rockets on the ground near U.S. missile silos. Graham would start with available technology and later employ more exotic defenses, such as laser weapons, if they proved out.

George A. Keyworth, Reagan's science adviser, said in an interview that sending laser beams from the ground to mirrors in space, where they would be reflected onto Soviet missiles shortly after launching, was "a very promising" concept.

John L. Gardner, director of defensive systems in the Pentagon's research office, said of the less ambitious--at least initially--High Frontier concept that it "does appear that it is certainly technically feasible." He put the cost at $50 billion to $75 billion or more.

Defense Secretary Caspar W. Weinberger has said that more money will have to be spent to carry out the president's mandate for a stepped-up anti-ballistic missile (ABM) effort, but he has not indicated how much, or on which projects.

"We're going to have to raise our sights considerably above mere fiscal thinking, because what you've got here is the possibility of wiping off the face of the earth not just one class of missile, but all of them," he said at a press conference in Madrid the morning after Reagan's speech.

Weinberger said he had no estimates of costs nor of what technologies would be pursued at a faster pace, but he expressed optimism that an effective missile defense would be found, declaring: "Bear in mind it was not really all that long ago that we didn't have an automobile, we didn't have airplanes and didn't even have television."

He said at his Pentagon news conference on Tuesday that a Pentagon executive committee had been formed to focus on ways to carry out the president's ABM mandate, but that no decisions on funding had been made.

"It is conceivable that we might redirect some of the funds from more or less traditional ground-based missile defense into more advanced systems . . . that can provide a reliable defense against incoming intercontinental ballistic missiles before they get near the ground . . . . ," Weinberger said.

Maj. Gen. Grayson D. Tate, manager of the Army's ABM program, told the Senate subcommittee that "we would like to be able to intercept Soviet missiles during the very early phases of their flight--the first five or six minutes, while they are still being powered and prior to the time they kick off all of the warheads and any penetration aids, such as balloons or decoys . . . . "