CAIRO, Egypt - Egyptian intelligence warned U.S. officials about a week before Sept. 11 that Osama bin Laden's terror network was in the advance stages of executing a significant operation against an American target, President Hosni Mubarak said Sunday.

Using a secret agent they had recruited who was in close contact with the bin Laden organization, Mubarak said, his intelligence chiefs tried unsuccessfully to halt the operation.

Mubarak said his intelligence officials had no indication what the target would be and had no idea of the magnitude of the coming attack.

"We didn't know that such a thing could take place," he said, referring to the Sept. 11 attacks. "We thought it was an embassy, an airplane ... the usual thing."

Mubarak's disclosure represents the first time a foreign leader has said that an intelligence service had penetrated bin Laden's network, al-Qaida, to the extent that discussions about specific operations - and whether they could be halted or postponed - were under way.

Mubarak said he believed that security at the U.S. Embassy in Cairo was tightened in early September as a result of the warning.

Mubarak cited the warning as evidence that Egypt has become an increasingly valuable intelligence partner to the United States in the war against terrorism, especially since Sept. 11. It seemed possible he was seeking to burnish Egypt's credentials, which have been questioned in Congress, in advance of his visit to Washington this week.

"Maybe some congressmen were thinking, 'What is Egypt doing?'" he said. "There are so many things we cannot say, mainly intelligence information. We did a lot, but sometimes you have to do it quietly."

A White House spokesman declined to comment on Mubarak's remarks. However, a senior U.S. intelligence official said the CIA had not received any warnings from Egypt about a possible attack in the days before Sept. 11.

"The Egyptians gave us some threat information, earlier in 2001, of possible attacks against U.S. or Egyptian interests," the official said. "There was nothing about hijackings, nothing about an attack inside the U.S. It did not come in the days before 9/11."

Mubarak's statements come as indications grow that U.S. officials were slow to interpret signs of an al-Qaida plot well before the attacks on the World Trade Center and the Pentagon.

Last week, FBI Director Robert S. Mueller III acknowledged lapses by his agency. And government officials disclosed Sunday that the CIA had learned about a Sept. 11 hijacker's connections to al-Qaida many months before the attacks.

By Mubarak's recollection, Egyptian intelligence officials informed U.S. intelligence between March and May 2001 of Egypt's penetration of al-Qaida. The agent established such close contact that Egyptian officials tried to use the agent's influence to stop the attack.

"We started to use them, to tell them, 'You can stop this,'" Mubarak said, to try "to give ourselves time to realize what may take place."

"I think this man, this agent, phoned the group of bin Laden," Mubarak said. The agent was told, "No, no, no, it's difficult to stop it."

By this time, "It was one week before" Sept. 11, "because the wheels were going on, we couldn't stop it - one week or four days, a very short time."