The Strategic Defense Initiative has produced no major breakthroughs since President Reagan called for development of a space-based defense against nuclear missiles three years ago, and much of the program's scientific progress has only deepened understanding of the difficulties of the undertaking, according to a Senate study to be released today.

The study reports that a space-based defense, also called "Star Wars," could face Soviet countermeasures 10 times more daunting than Defense Department officials projected less than two years ago. As a result, the project is probably not feasible without Soviet acquiescence, according to government scientists.

In addition, launching and servicing the thousands of battle stations that would be needed in space may be as difficult as developing the exotic weaponry itself. With today's prices and technology, 2,000 shuttle flights and between $87 billion and $174 billion would be needed to launch the hardware into orbit, according to early estimates.

The 62-page report, an unclassified version of which was obtained last week, disputes Lt. Gen. James A. Abrahamson's contention that the program has been proven "technically feasible" and will be ready for a development decision in the early 1990s. Abrahamson, director of the Pentagon's SDI Organization, has said that "only a few diehards" question the program.

Many scientists and program managers working for SDI do not support that view, according to the report, although they support the research effort.

"If anything, these working scientists resented the fact that the progress their research has achieved has been inflated, because it undermines their credibility as scientists," the report concludes. "One researcher said the hyping of the progress 'is driving good people out of the program.' "

The Senate report is based on interviews with officials and researchers at the SDI Organization, the Army's Strategic Defense Command, the Air Force Space Division and two of the nation's three weapons laboratories, Sandia and Lawrence Livermore. It was written by aides to three Democratic members of the Senate Appropriations Committee -- Lawton Chiles (Fla.), J. Bennett Johnston (La.) and William Proxmire (Wis.) -- who have supported SDI research but at lower funding levels than the administration has sought.

Telephone calls to the SDI organization for comment were not returned Friday. Proxmire said the Pentagon, which wrestled with the report for several weeks before declassifying most of it, considered it unbalanced in its opposition.

"Obviously, we're critics of SDI," Proxmire said. "It's no more balanced than their testimony before the committee has been."

But Proxmire said the report demonstrates "the enormous vulnerability of these space-based battle stations" and the cost of "lifting this colossal amount into orbit."

"That could cost hundreds of billions of dollars, and that's just the beginning," he said. "It has to be maintained, it has to be constantly modernized. . . . We're going to have to lift a garage into space."

SDI is envisioned as interlocking systems of weapons and sensors in space and on the ground that would attempt to destroy Soviet nuclear missiles as they are launched, as they coast through space and as they enter the atmosphere over the United States. When he called for SDI in March 1983, Reagan said it could "set us free from the prison of nuclear weapons."

Since then, the Defense Department has outlined the largest military research program in its history. The SDI office is seeking $4.8 billion for research in fiscal 1987, more than the total research and production costs for many weapon systems.

The effect of increased spending in the past three years, according to the Senate report, has been to underline the challenges.

Most scientists agree, for example, that the system will not work unless many missiles can be destroyed as they are launched, before they disgorge thousands of warheads and decoys in space. For "boost phase kill," however, SDI would need thousands of battle stations and satellites in space, which would themselves be vulnerable to Soviet attack.

SDI is studying "hardening" satellites to attack, having them maneuver to evade attack, giving them "shootback" capability and launching so many thousands of them that the Soviets could not attack enough of them. Each of those solutions would increase cost and weight, however, and could face Soviet counter-countermeasures.

"In our briefings, we asked repeatedly how our space-based elements would be protected from Soviet space mines," the report says. "We never received a plausible answer."

Most exotic weapons being developed to destroy missiles, moreover, such as lasers and particle beams, would be more useful for knocking out satellites and other components of a space-based defense, the report says.

"Scientists at the Sandia Laboratory . . . have come to the conclusion that space-based, boost-phase defense can never be made survivable, unless by treaty," it adds.

One scientist at Sandia said the only solution would be joint U.S.-Soviet battle stations in a plan dubbed MIMAS, for Mutually Implemented Mutually Assured Survival. The report finds it "difficult to imagine" such cooperation.

If SDI must rely on "mid-course" attack, the problems become even more serious, according to recent evaluations. SDI officials initially predicted the Soviets could produce "a threat cloud of tens of thousands of warheads and decoys." Although new estimates are classified, the report notes that more recent "threat scenarios" are "ten times as great and far more complicated."

"The problem of discriminating warheads from decoys . . . is much larger than Congress has been led to believe," the report says.

Finally, for defense to be cheaper than offensive countermeasures that could overwhelm it, the military-industrial complex would have to undergo a revolution, officials told the Senate investigators. Through "Henry Ford production techniques," satellites that now cost hundreds of millions of dollars would have to cost millions; missiles, which now cost millions (each MX costs $70 million), will also have to cost far less.

"It appears that the transportation-support-logistics system for a comprehensive strategic defense may well be as complex and unprecedented as the defense itself," the report says.