Blair also indicated at a news conference he was taking a harder line alongside the United States in Washington's demand for a "regime change" in Baghdad, a position that could take a military invasion to bring about.
"Either the regime (of Saddam) starts to function in an entirely different way -- and there hasn't been much sign of that -- or the regime has to change," the British leader said. "That is the choice, very simply."
Blair said Iraq "poses a real and unique threat" to the entire world. "It continues to develop weapons of mass destruction. We have to face up to it, we have to deal with it."
Asked to produce some evidence, the prime minister said his government has spent months compiling a dossier against Saddam and that "the best thing to do is to publish that in the next few weeks," to prove that Iraq possesses chemical and biological weapons and that it is seeking to develop nuclear weapons technology.
Government officials earlier this year said such a document was being prepared. But as months have gone by without its release, opposition to British participation in any U.S.-led military action against Iraq has grown to worrisome proportions for Blair.
Some 160 members of Parliament, many of them from Blair's own ruling Labor Party, have signed a motion opposing British involvement in any military campaign against Iraq, and as many as three members of his Cabinet are said poised to quit over the action.
Meanwhile, a series of public opinion polls during the past week have shown that from 52 percent to 71 percent of Britons are against a war on Iraq. Even in Sedgefield, Blair's own constituency in northeast England where he had Tuesday's news conference, a regional newspaper survey showed 54 percent of voters opposed his stance on Iraq.
Blair attributed much of the opposition to "anti-Americanism -- I think there's a lot of that around." Defending his own alignment with President George W. Bush, he said, "America shouldn't have to face this issue alone."
Stung by criticism in some quarters that he was the American leader's "poodle," Blair insisted: "I would never support anything I thought was wrong just out of blind support for the United States."
Blair declined to confirm or deny published reports he planned to meet with Bush for face-to-face talks -- probably in Washington or at Camp David, Md. -- sometime this month.
"I don't want to comment on when any meetings will take place," Blair said.
He repeated several times the threat posed by the Iraqis.
"They will acquire whatever weapons they can," he said.
He added that his government's dossier showed Baghdad already has stockpiles of chemical and biological weapons and that "there is some evidence" that it is seeking to acquire nuclear weapons.
Blair reiterated his demand that U.N. inspectors be allowed in by Iraq to inspect its weapons.
"There is no negotiation about this," he said, referring to Baghdad's comments that it might be willing to talk about the issue in inspectors.
"They know what they have to do," the prime minister said.
In Johannesburg, South Africa, Iraqi Deputy Prime Minister Tariq Aziz said Tuesday his country would discuss the return of weapons' inspectors but only if a dialogue regarding Iraqi sovereignty over its territory and end to sanctions were also part of the program.
"If there is to be a solution, there should be a solution for all of the important issues in Iraq," he said in a statement. "It is not possible to select just one aspect and address only that."
The proposal is similar to previous Iraqi proposals and, according to U.N. Secretary-General Kofi Annan, is unacceptable.
"The return of inspectors must be unconditional," Annan said after meeting with Aziz.
Meanwhile, Blair added, there is a string of nine U.N. resolutions with 27 demands -- 23 of which Baghdad hasn't met -- still on the table to be dealt with.
Blair sidestepped a question as to whether the Anglo-American alliance would seek a U.N. mandate before going ahead with any military action against Iraq.
"The important thing," he said, "is that the U.N. has to be a route to deal with this problem. Not a way of avoiding dealing with it."