One month before the United States bombed the El Shifa pharmaceutical plant in Sudan, CIA analysts said more testing would be needed before they could firmly conclude that the plant was producing a key component of deadly VX nerve gas, as the Clinton administration maintained on the night of the strike.

The bombing, one year ago this week, has led to a lawsuit by the plant's owner, an embarrassing series of retractions by top U.S. officials, and an increasingly pressing question: Just how certain does the government need to be before it uses force against a suspected terrorist group overseas?

The Clinton administration continues to defend the airstrike, which killed a night watchman and destroyed the pharmaceutical factory in Khartoum, Sudan's capital. But senior officials now concede that the plant did, in fact, make some medicines. They also acknowledge that it may not have manufactured chemical weapons -- at least at the time of the bombing.

President Clinton ordered the missile strike in retaliation for Saudi millionaire Osama bin Laden's alleged role as the mastermind in the terrorist bombing of two U.S. embassies on Aug. 7, 1998. The twin truck bombs in Kenya and Tanzania killed more than 200 people, including 12 Americans.

To strike back, U.S. Navy ships fired 13 Tomahawk cruise missiles at El Shifa and 66 missiles at bin Laden's training camps in Afghanistan. The attack was timed to coincide with a meeting of bin Laden's key operatives at one of the camps.

Since the attack, senior administration officials have stood behind what they continue to describe as a "compelling" piece of evidence: a soil sample, secretly obtained near the El Shifa site by a CIA operative, that was found to contain a high concentration of EMPTA, a chemical that does not occur in nature and has no use except in making nerve gas.

"Nothing that we've learned subsequent to the attacks has led anybody to [conclude], if they had to do it over again, that they would make a different decision," one senior administration official said this week.

However, in a three-page analytical paper written late last July, well before the embassy bombings or the retaliatory targeting of El Shifa, CIA analysts raised questions about what conclusions could safely be drawn from the soil sample.

According to officials familiar with the paper, the CIA analysts considered the presence of EMPTA to be a virtually sure-fire indicator that the plant had something to do with chemical weapons. But they could not be sure whether the plant actually manufactured VX or merely served as a warehouse or transshipment point for chemicals used in making nerve gas. Nor could they be sure how recently that activity might have occurred.

The paper, which was reviewed at senior levels in the CIA and disseminated to the National Security Council staff, recommended covert efforts to obtain more soil samples to try to answer those questions.

Intelligence officials also said in interviews this week that even if El Shifa did make nerve gas, they cannot explain why a high concentration of EMPTA would have been present in the soil outside the plant. EMPTA is a viscous substance that is not volatile enough to vaporize, and the plant's drainage system is unlikely to have deposited effluent in surface soil on its periphery.

That uncertainty, the officials said, is another reason why CIA analysts recommended additional soil sampling at the site last July.

Still, the intelligence officials played down the importance of that recommendation and said CIA Director George J. Tenet did not mention any need for further testing when he presented senior policymakers with a "mosaic" of intelligence to support the targeting of El Shifa at a White House briefing on Aug. 17, 1998, three days before the U.S. missile strike.

Tenet's chain of evidence, they said, consisted of:

Financial records enabling CIA analysts to "follow the movement" of millions of dollars from bin Laden to Sudan's state-owned Military Industrial Corp. in the mid-1990s.

"Highly reliable intelligence" indicating that bin Laden had reached an agreement with the Sudanese government, which is on the State Department's list of state sponsors of terrorism, enabling him to produce chemical weapons in Sudan with government assistance under certain conditions.

Frequent visits by officials linked to El Shifa's original owner to Samara Drug Industries in Iraq, a pharmaceutical firm closely linked to the head of Iraq's program for producing VX from EMPTA.

And, finally, the soil sample containing a high concentration of EMPTA gathered near the El Shifa plant by an operative who had been carefully polygraphed and vetted by his CIA handlers.

The officials denied published reports that the operative was an Egyptian or an agent of the Egyptian intelligence agency. They said they still have full confidence both in the "CIA asset" who collected the sample and in the chemical analysis of the sample by an independent laboratory, which they characterized as "95 percent" reliable.

One intelligence official said Tenet's analysis, which came after the embassy bombings, had moved "light-years" beyond the July document recommending further sampling.

"With information that bin Laden had attacked Americans before and planned to do so again, that he was seeking chemical weapons to use in future attacks, that he was cooperating with the government of Sudan in those efforts, and that Sudan's El Shifa plant was linked to both bin Laden and chemical weapons, we had a responsibility to counter this threat," White House press secretary Joe Lockhart said in a statement Thursday.

But even in defending the attack, one administration official said that national security adviser Samuel R. "Sandy" Berger and Defense Secretary William S. Cohen made "inaccurate" statements on the night of the attack when they said they were certain that El Shifa produced EMPTA.

"We never had any evidence of that," the official said. "The correct statement, and it has been corrected, was that EMPTA was present at the plant."

The official also noted a substantial change in the administration's position with regard to the plant's owner, the wealthy Saudi businessman Saleh Idris: The U.S. government no longer claims that he is a terrorist.

Shortly after the missile strike, administration officials conceded that they had not realized Idris owned the plant, which he had acquired six months earlier. Nevertheless, the Treasury Department moved almost immediately to freeze $24 million he had on deposit at the Bank of America. The freeze was lifted in May, after Idris filed suit in federal court and the government did not contest the case.

Idris has said he now intends to file a second suit, seeking $30 million in compensation for the plant. It is unclear whether the government will contest it.

One senior administration official maintained in an interview this week that Idris's case is "irrelevant" to the justification for striking the plant.

"Even if you took his view, that he owned it and he's an innocent guy, as long as we believe, and continue to believe, that this was a resource associated with chemical weapons that was available to bin Laden, Idris's innocence or guilt, and his intentions, really don't have anything to do with it."

Idris's lawyer, Mark J. MacDougall, a partner at Akin, Gump, Strauss, Hauer & Feld, responded that there is no evidence linking El Shifa to the Military Industrial Corp., under Idris or the plant's previous owner.

The administration's explanation for the El Shifa attack "has changed dramatically during the past year," MacDougall said. "Either the evidence supporting the decision to destroy the plant exists, or it doesn't. Until the facts are disclosed, and tested, this is not going to go away."