The countdown has begun for Saddam Hussein to withdraw his troops from Kuwait or face a U.N.-authorized attack, but the Iraqi leader has shown no sign of bowing to the pressure.

In its strongest action yet in the crisis, the United Nations Security Council voted Thursday to allow the use of force against Iraq if it does not pull its troops out of Kuwait by Jan. 15.The Security Council voted 12-2 with China abstaining and Cuba and Yemen voting against the resolution. It was the first time since July 1950, when the council authorized a unified command against North Korean aggression in South Korea, that the body had endorsed the use of military power.

Iraq Friday called the resolution "illegal, null and void" because it said it was imposed by the United States.

"It is first and foremost an American decision in which certain powers participated only under American pressure," said Baghdad radio, monitored in Nicosia. "The United States practiced all forms of pressure, terrorism and bribes" to pass it.

The resolution said Iraq has refused to comply with U.N. resolutions for it to quit Kuwait "in flagrant contempt of the council" and gave Iraq "one final opportunity, as a pause of good will," to withdraw its 400,000 troops that have occupied Kuwait since Aug. 2.

Secretary of State James Baker joined foreign ministers Eduard Shevardnadze of the Soviet Union, Douglas Hurd of Britain and Roland Dumas of France in calling for renewed diplomacy to persuade Saddam to withdraw.

The four ministers, using similar language, said the Security Council would not take any further action against Iraq until Jan. 15, "assuming no adverse change in circumstances.""We do so while retaining our rights to protect our foreign nationals in Iraq and mindful of the terms of the Fourth Geneva convention and the Geneva Protocol of 1925, should Saddam Hussein use chemical or biological weapons," Baker said.

President Bush called the resolution "a very powerful statement and everybody ought to understand how strong it is and how important it is. Everybody wants a peaceful resolution. I think this would drive home the point to him that he's got to get out of Kuwait," he said.

Shevardnadze said the Soviet Union was unlikely to send troops to the Middle East and, displaying a frankness unimaginable a year ago, added, "The memories of Afghanistan and Czechoslovakia are still fresh in the minds of our citizens."

But Shevardnadze said, "If even one Soviet citizen (in Iraq) is harmed, I cannot say what the consequences would be, but it will be very serious."

The Pentagon wasted little time reacting to the U.N. resolution, planning to build up its forces for possible offensive action after Jan. 15 by sending another 300 warplanes to the gulf. That will increase the Air Force's fleet of planes in the area to 1,200 planes, the Los Angeles Times reported Friday.

Citing unnamed defense sources, the newspaper said the new wave of planes will include a second squadron of F-117 Stealth fighters, F-15E ground-attack jets, F-16 fighters, A-10 tank-killers, refueling tankers and RF-4C photo-reconnaisance planes, the sources said.

A total of 27 more Air Force units with about 10,000 personnel will be deployed in the region, beginning as early as this week. Some will be redeployed from Europe and others will come from U.S.-based reserve and Air National Guard units, the newspaper said.

In a speech condemning the U.N. resolution and saying Iraq would fight "ferociously" in the event of attack, Saddam said Iraq had the ability to detect Stealth fighters, which are designed to be invisible to radar.

Former Navy Secretary James Webb said if Bush is serious about going on the offensive he should resume the draft and seek a declaration of war from Congress.

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(Additional information)

Text of U.N. resolution authorizing force

The Security Council, recalling and reaffirming its resolutions 660, 661, 662, 664, 665, 666, 667, 669, 670, 674 and 677 (of 1990).

Noting that, despite all efforts by the United Nations, Iraq refuses to comply with its obligation to implement Resolution 660 (1990) and the above subsequent relevant resolutions, in flagrant contempt of the council, mindful of its duties and responsibilities under the Charter of the United Nations for the maintenance and preservation of international peace and security, determined to secure full compliance with its decisions, acting under Chapter VII of the Charter of the United Nations:

1. Demands that Iraq comply fully with Resolution 660 and all subsequent relevant resolutions and decides, while maintaining all its decisions, to allow Iraq one final opportunity, as a pause of good will, to do so;

2. Authorizes member states cooperating with the government of Kuwait, unless Iraq on or before 15 January 1991 fully implements, as set forth in paragraph 1 above, the foregoing resolutions, to use all necessary means to uphold and implement Security Council Resolution 660 and all subsequent relevant resolutions and to restore international peace and security in the area;

3. Requests all states to provide appropriate support for the actions undertaken in pursuance of paragraph 2 of this resolution;

4. Requests the states concerned to keep the council regularly informed on the progress of actions undertaken pursuant to paragraphs 2 and 3 of this resolution;

5. Decides to remain seized of the matter (keep the matter under active consideration).