The top nuclear inspector conceded Wednesday that aluminum tubes the Iraqis had sought for rockets could be modified for a nuclear program, as President Bush reasserted in his State of the Union address.

"We believe the tubes were destined for the conventional rocket program," Mohamed ElBaradei told The Associated Press in an interview. "They could be used for enrichment but they need substantial modification before they could be used."

He said such a process would be expensive, time-consuming and detectable but that the Iraqis have the capabilities to alter the tubes.

ElBaradei told the Security Council in a report Monday that he had found no evidence Iraq had revived its nuclear program. The comments, coupled with his determination that the tubes were for rockets, put him at odds with the Bush administration which has insisted the tubes were meant for enriching uranium.

The back-and-forth between the Bush administration and ElBaradei's International Atomic Energy Agency began shortly after the president first raised the Iraqi attempts to buy the materials when he addressed the United Nations last September.

As a result, ElBaradei made it a top priority for his team to investigate the matter when inspections resumed two months later.

Iraq admitted they sought the tubes but said they were for a rocket program and very quickly, the nuclear team began to agree.

But the United States has been relentless in its insistence that the tubes were for a nuclear program and President Bush included it again in his annual address Tuesday.

"We believe...that these tubes are of the fineness and kind of tooling and workmanship that is definitely consistent with the use of enriching uranium," U.S. Ambassador John Negroponte said Wednesday.

"The way in which Iraq has gone about trying to procure those tubes suggests quite clearly that they were trying to do something illicit," he told reporters

He and other peppered ElBaradei with questions about the tubes again Wednesday during a closed-door Security Council meeting.

"What ElBaradei said is that the first tubes they looked at ... were clearly not of the type [for enrichment] but that some others might have been," said British Ambassador Jeremy Greenstock.

ElBaradei's upbeat assessment of Iraq's cooperation Monday was in sharp contrast to that of his U.N. counterpart, Hans Blix, who was tougher on Iraqi cooperation and suggested Baghdad may be hiding deadly biological agents.

But both men cast doubt Wednesday on President Bush's claims in the State of the Union that Iraqi spies had penetrated the inspections.

"I don't think anyone at a high level would contend that there have been leaks," Blix told reporters.

The president said intelligence sources had revealed that Iraqi security personnel are at work hiding documents and materials from the U.N. inspectors, sanitizing inspection sites and monitoring the inspectors themselves.

ElBaradei said security was tight among inspectors but he wouldn't be surprised if the teams had been infiltrated by any country eager to know what exactly is going on, and not necessarily by the Iraqis.

"We are used to many efforts of infiltration but I will not be shocked if we have been infiltrated. We're trying to have a very tight security plan on a need-to-know basis and any intelligence we get is shared with not more than three or four people maximum."

ElBaradei also dismissed Bush's claims that intelligence agents are posing as scientists wanted for interviews with inspectors, saying it's unlikely the inspectors "could be fooled."

"We know all the scientists from the past and I think our people could easily detect if that person is a scientist or not."

In his State of the Union, Bush said: "Iraqi intelligence officers are posing as the scientists inspectors are supposed to interview. Real scientists have been coached by Iraqi officials on what to say and intelligence sources indicate that Saddam Hussein has ordered that scientists who cooperate with U.N. inspectors in disarming Iraq will be killed, along with their families."