State Department and embassy officials had adequate intelligence warnings of a possible terrorist attack on U.S. facilities in Beirut but failed to respond, according to a House intelligence committee report on the Sept. 20 bombing of the U.S. Embassy annex in Beirut.

In the sharply worded report, released yesterday, the Permanent Select Committee on Intelligence found "no logical explanation" for the lack of effective security at the annex.

It said intelligence reports "portrayed a situation where those responsible for security at U.S. installations in Beirut -- both in Washington and on the scene -- should have been on full alert and should have taken every precaution possible to thwart just such an attack as occurred."

The report's conclusions directly contradict President Reagan's assertion that administration officials had been hampered in protecting the embassy by inadequate intelligence caused in part by intelligence cutbacks in previous administrations.

Reagan's statements on the bombing, which killed at least 20, including two Americans, have become a major issue in the presidential campaign. Democrats have accused him of trying to avoid responsibility for the bombing by blaming former president Jimmy Carter and others.

In an unusually specific response to Reagan's assertions, the report states that not only were intelligence reports "adequate" but intelligence budgets have steadily increased since 1979 and "adequate resources" are now devoted to the collection of intelligence on terrorism.

House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), who requested the committee investigation, said yesterday that Reagan can no longer make such excuses. "The president must stop trying to sweep this tragic incident under the rug," O'Neill said.

In the past, State Department officials have acknowledged that security at the annex in east Beirut was not complete when embassy personnel moved there July 31.

But they said they believed the new building was much safer than the British Chancery building in west Beirut, where a temporary U.S. Embassy had been set up after the 1983 car bombing of the official U.S. Embassy.

The intelligence report was approved by both Republicans and Democrats on the committee before it was released. According to several committee members, all of them were "astounded" at the lack of security measures at the annex in light of previous vehicle bombings of U.S. facilities in Beirut.

The report deals primarily with the question of whether the intelligence community was at fault in the suicide bombing. It draws the following conclusions:

*Beirut had become so hostile to Americans that embassy officials should have viewed it as a "war zone" and taken adequate precautions. Based on the success of two previous suicide vehicle bomb attacks -- first at the U.S. Embassy and then at the U.S. Marine encampment -- embassy and State Department officials should have used "common sense" to realize that further vehicle bombs were likely.

*Intelligence performance in dealing with the threat related to the bombing was "adequate."

Having been criticized after the Marine bombing for passing along too much, often unreliable, information, intelligence agencies this time provided specific "alerts" -- highlighting "likely" terrorist acts -- to embassy officials.

The Defense Intelligence Agency and State Department intelligence officials provided alerts about "two September threats against American personnel in Beirut that . . . should have gained the direct attention of top State Department and embassy officials."

*In addition, there were credible reports during the two months before the bombing that terrorist groups, particularly radical Shiite groups connected to Iran, were planning attacks against U.S. officials and installations.

These reports did not specify a time or place for the attacks but they "should have heightened and reinforced the concern of all U.S. officials responsible for the safety of the American Embassy personnel in Beirut."

The report does not directly criticize a decision to remove an 80-man Marine contingent that had been guarding embassy personnel before the move to the annex on July 31.

But it questions why the State Department or administration officials did not request an assessment from intelligence sources of the effect on security of the Marines' removal, especially after the DIA raised concerns about the reliability of local guards hired to protect the annex.

The report also states that intelligence officials have identified a terrorist group as being responsible for the annex bombing. It said the group, which it did not name, may have received support from Iran.