A new study of the Patriot missile, apparently based on full access to classified Army records from the Persian Gulf War, yesterday said there is strong evidence to confirm that the Patriot destroyed incoming Iraqi Scud missile warheads in only 9 percent of all engagements.

The study by the General Accounting Office was the latest in an embarrassing series of reassessments of what was once portrayed as the preeminent performer of the gulf war's technology showcase. The study passed no judgment on the percentage of Patriots that struck their targets, but said claims for "warhead kills" higher than 9 percent could not be supported by reliable evidence.

Because the Patriot "was operating in a war zone rather than on a test range," the study left open the possibility that its rigorous standards of evidence understated the Patriot's success. The study also did not address the Patriot's psychological value against an Iraqi weapon used principally for political and psychological effect.

But the Patriot's scorecard of hits and misses has long since acquired a symbolic importance that transcends such qualifiers. Senior Pentagon officials have wielded the Patriot in a public relations campaign against critics of big-ticket, high-technology weapons, particularly the controversial Strategic Defense Initiative to develop a missile defense system against nuclear weapons.

Gen. H. Norman Schwarzkopf, commander in chief of allied forces, said two weeks after the gulf war began in January 1991 that "the Patriot's success, of course, is known to everyone; it's 100 percent so far."

In dozens of ensuing public appearances, Defense Secretary Richard B. Cheney has used the Patriot as his principal proof that "a decade of gloom-and-doom reporting" about military technology was wrong.

Additional studies, particularly by MIT scientists George N. Lewis and Theodore A. Postol, forced the Army to issue downward revisions of Patriot's success rates -- first to 80 percent in Saudi Arabia and 50 percent in Israel, then to 70 percent in Saudi Arabia and 40 percent in Israel.

Yesterday's study, commissioned by Rep. John Conyers (D-Mich.), a Patriot critic, assessed the Army's most recent claims, released in April. The GAO disclosed that the Army had "high confidence" of warhead kills in only 25 percent of Patriot engagements. But except in 9 percent of the cases, the GAO said, the Army could prove only that "the Patriots came close to the Scuds," not that they destroyed them.

Significantly, Pentagon spokesman Pete Williams yesterday declined to take issue with the GAO report, saying that its "nitpicking and hand-wringing" would be "a little more on target if in fact the Patriot was designed originally as an anti-missile defense. It wasn't."

Actually, an advanced version of the Patriot -- the one deployed in the gulf -- was designed for missile defense and was tested in that role in 1986.