The Pentagon has changed the Strategic Defense Initiative and new early-warning radar programs to stay within provisions of the 1972 antiballistic missile treaty during the Reagan administration, according to a new study by the National Campaign to Save the ABM Treaty.

The study says, however, that tests planned for 1989 under the so-called "Star Wars" research program "will come into conflict with the ABM treaty limits."

The study also reviews U.S. government charges of Soviet violations of the treaty and finds that the new large radar facility being built in central Siberia is "inconsistent" with the treaty provisions. But it concludes that U.S. fears that the facility could lead to a ballistic missile defense are exaggerated.

"It would have questionable utility when faced with the U.S. missile threat of the 1990s," the study says.

Overall, the analysis concludes that "present and future U.S. and Soviet antimissile systems threaten the continued viability of the ABM treaty."

The group is headed by Ambassador Gerard Smith, chief negotiator of the ABM treaty. The report was compiled by John B. Rhineland, legal counsel to the SALT I delegation, John E. Pike of the Federation of American Scientists and Thomas K. Longstreth.

Release of the private study comes as sources said yesterday that a congressionally mandated Pentagon report on the president's Star Wars program has been delayed. Under the fiscal 1985 appropriation bill, the Pentagon was directed to send a study to Congress by March 15, detailing SDI's costs and analyzing how it would affect the ABM treaty.

Congressional aides said yesterday that a classified summary of the report may reach Capitol Hill late this week but that there was no estimate on when an unclassified version would be available.

A House Foreign Affairs subcommittee has canceled a hearing that was to have been held today to review the reports of the Pentagon and the National Campaign to Save the ABM Treaty.

In January 1984, according to the study, President Reagan signed National Security Decision Directive 119, which ordered that SDI programs "remain in compliance with the ABM treaty" through 1988.

Two so-called demonstration programs, scheduled to be carried out in 1987-88 were delayed. Launching Talon Gold, a space-based pointing and tracking system to guide laser beams, was put off till 1990, although a portion of it will be ground tested in the interim. The Airborne Optical System, a target designator to be carried on an airplane, was rescheduled for testing in 1989.

According to the study, "some administration officials now appear to accept that the treaty would have to be amended or abrogated in order for many of the demonstrations planned from 1989-93 to take place."

It quotes SDI director Air Force Lt. Gen. James A. Abrahamson telling the House Armed Services Committee, "At some point, however, we would have to depart from the treaty" when current testing can no longer be done in laboratories." Abrahamson went on to say that would be necessary "about the turn of the next decade."

While the United States has protested the new Soviet phased-array radar, the study notes that two planned U.S. early-warning radars have been modified in the last year to make them conform more closely with the treaty.

The two radars, nicknamed Pave Paws, would be built in Georgia and Texas and are designed to watch for sub-launched ballistic and sea- or air-launched cruise missiles approaching the U.S. mainland from the south.

Initial deployment plans for these two facilities would have resulted in radar coverage of two-thirds of the continental United States, something the study said would be "inconsistent" with ABM treaty limitations.

The radar sweep of these facilities has been reoriented, the study said, to narrow their coverage.

Two additional phased-array radars, planned by the United States for Greenland and England, also are discussed as possible sources of ABM treaty problems. The facilities would upgrade existing, less capable facilities, but their construction, the study says, would offer the Soviets' new opportunities to question U.S. activities.

Moscow, the study notes, complained in 1975 about a U.S. phased-array radar being placed on Shemya Island off Alaska and three years later criticized the first two Pave Paws facilities in California and Massachusetts.

To solve the conflicts over phased-array radars, the study recommends that the two sides freeze all such facilities at present levels and prohibit new ones from being completed.

It also recommends that such radars, which can perform various tasks from providing early warning to managing a ballistic missile defense, be delayed unless the parties agree on their construction.