Washington ? Saddam Hussein is aggressively seeking nuclear and biological weapons and “the United States may well become the target” of an attack, Vice President Dick Cheney said Sunday as the Bush administration pressed its case for toppling the Iraqi leader.

Cheney and top administration officials took to the Sunday talk shows as part of President Bush’s effort to convince the public, Congress and other countries that action against Saddam is urgently needed. The officials cited the Sept. 11 attacks in making the case that the world cannot wait to find out whether the Iraqi president has weapons of mass destruction.

Vice President Dick Cheney discusses the Bush administration's case for action against Iraq on Sunday on NBC's Meet

“The problem here is that there will always be some uncertainty about how quickly he can acquire nuclear weapons. But we don’t want the smoking gun to be a mushroom cloud,” national security adviser Condoleezza Rice told CNN’s “Late Edition.”

Added Defense Secretary Donald Rumsfeld on CBS’s “Face the Nation”: “Imagine, a September 11 with weapons of mass destruction. It’s not 3,000; it’s tens of thousands of innocent men, women and children,”

Cheney said on NBC’s “Meet the Press” that the United States was justified in striking any country it believes is planning an attack against America, applying the Bush administration’s new foreign policy doctrine on pre-emptive military action to Iraq.

Cheney, citing unspecified intelligence gathered during the past 12 to 14 months, said Saddam had the technical expertise and designs for a nuclear weapon, and had been seeking a type of aluminum tube needed to enrich uranium for a weapon. The tubes have been intercepted through one known channel, Cheney said.

Cheney said he did not know for sure whether Saddam already had a nuclear weapon. Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said he did not think so.

Bush will address the United Nations on Thursday to build his case for action against Iraq. Secretary of State Colin Powell said whatever the United Nations decides, Bush will reserve the right to go at it alone against Iraq.

Critics, some of them in countries allied with the United States, have questioned whether military action to achieve the U.S. government’s goal of overthrowing Saddam Hussein from power is legal.

Iraq’s vice president denied Sunday that his country was trying to collect nuclear materials.