Blair told reporters that coalition forces had identified about 1,000 suspicious Iraqi weapons sites but rebuilding the country was a bigger priority than finding illegal arms.
"There isn't any doubt that Iraq has had weapons of mass destruction," the British prime minister said at his monthly news conference. "That is not in dispute, not by anybody. I remain confident they will be found."
Saddam's alleged program to develop biological, chemical and nuclear arms was the main justification for U.S.-led war that ousted the Iraqi dictator.
But no such weapons were used against coalition forces, and Blair's critics say the failure so far to find illicit arms proves war was unnecessary.
Since the war began, U.S. troops have reported finding chemical protective suits, antidotes to chemical weapons and written plans for chemical warfare, but no actual biological or chemical weapons.
Several potential finds have been reported and then discounted. Tests are ongoing on other recent finds.
Initial tests on a 55-gallon drum found in an open field near the northern Iraqi town of Baiji this weekend indicated it might contain the nerve agent cyclosarin and a blister agent that could be mustard gas. The New York Times reported subsequent tests proved negative.
Blair suggested Saddam hid his banned weapons before the arrival of U.N. inspectors.
"If they were systematically concealed, they might not have been available for use in a conflict," he said. "It does not in the least follow from that that they couldn't have been reconstituted had we all left Iraq and the weapons inspectors not been able to carry out their job."
Last week, six Iraqi scientists and several graduate students say they were told immediately before the war to destroy or hide biological research. They claim the research was for civilian purposes only.
In addition, The Times reports that an Iraqi scientist has told coalition troops that Iraq began destroying biological and chemical materials in the months before the war, and sent some weapons to Syria.
Blair's approach mirrored recent statements by U.S. leaders. Last week, President Bush said "it's going to take time to find" the weapons, and hinted that actual weapons may have been eliminated before or during the war.
"Whether he destroyed them, moved them, or hid them, we're going to find out the truth," the president said.
Some 1,000 experts are involved in the search for weapons. Blair said there was a need for a process of "independent verification" of Iraq's weapons program but didn't say whether he believed that task should fall to the United Nations. The U.S. has resisted any extensive U.N. role in the weapons hunt.
Blair appeared to suggest that although Saddam might not have used weapons of mass destruction in combat, the arms risked getting into the hands of terrorists.
"As more intelligence emerges, in particular from inside Iraq and the former Iraqi intelligence unit, I think you will find increasing evidence of links between the previous Iraqi regime and terrorist organizations," he said.
But despite the worry about proliferation, the Los Angeles Times last week reported that the U.S. military left a major civilian nuclear research site — one known to hold radioactive materials that could be used for a dirty bomb — unguarded for days, then secured it but did not search it to see what was missing.
Part of the Bush administration's justification for going to war was its allegation that Iraq had ties to terror groups, including al Qaeda. Last week, U.S. officials announced the capture of Farouk Hijazi, a former high-ranking Iraqi intelligence official with possible al Qaeda links.
Papers found Saturday by journalists working for the Sunday Telegraph reveal that an al Qaeda envoy met with officials in Baghdad in March 1998, the newspaper reported.