WASHINGTON -- Any "pre-emptive, unilateral use of military force to overthrow the government of Iraq" cannot be justified at this time, the U.S. bishops told President Bush.

The bishops urged Bush "to step back from the brink of war and help lead the world to act together to fashion an effective global response to Iraq's threats."

In a letter to Bush, the bishops used Catholic just-war criteria to argue that unilateral strikes against Iraq would differ from the use of force against Afghanistan, part of a broader war against terrorism in response to Sept. 11 terrorist attacks on the United States.

"Given the precedents and risks involved, we find it difficult to justify extending the war on terrorism to Iraq, absent clear and adequate evidence of Iraqi involvement in the attacks of Sept. 11 or of an imminent attack of a grave nature," the bishops said.

The letter, dated Sept. 13 and released in Washington Sept. 17, was signed by Bishop Wilton D. Gregory of Belleville, Ill., president of the U.S. bishops' conference, on behalf of the bishops' Administrative Committee.

Addressing the U.N. General Assembly Sept. 12, Bush said action against Iraq would be unavoidable unless the United Nations forced the Mideast nation to disarm. He challenged the general assembly to compose a new resolution on Iraq or face the possibility of unilateral action by the United States.

Iraq announced Sept. 16 it would allow, without conditions, the return of U.N. weapons inspectors.

In the bishops' letter, Bishop Gregory said the "Catechism of the Catholic Church" limits the just-war criterion of "just cause" to "cases in which the damage inflicted by the aggressor on the nation or community of nations is lasting, grave and certain."

"Is there clear and adequate evidence of a direct connection between Iraq and the attacks of Sept. 11 or clear and adequate evidence of an imminent attack of a grave nature?" he wrote. "Is it wise to dramatically expand traditional moral and legal limits on just cause to include preventive or pre-emptive uses of military force to overthrow threatening regimes or to deal with the proliferation of weapons of mass destruction? Should not a distinction be made between efforts to change unacceptable behavior of a government and efforts to end that government's existence?"

He said the moral credibility of force depends on legitimate authority and, as such, "decisions of such gravity require compliance with U.S. constitutional imperatives, broad consensus within our own nation, and some form of international sanction, preferably by the U.N. Security Council."

He added that war against Iraq could result in dangerous and unpredictable effects upon Iraqi civilians and Middle East stability, in violation of the criteria of the "probability of success" and "proportionality."

"Would ... force succeed in thwarting serious threats or, instead, provoke the very kind of attacks that it is intended to prevent?" he wrote. "How would another war in Iraq impact the civilian population, in the short- and long-term? How many more innocent people would suffer and die, or be left without homes, without basic necessities, without work?