LONDON, JAN. 7 -- Secretary of State James A. Baker III will use his meeting Wednesday with Iraq's foreign minister to present a message, including a graphic letter from President Bush, designed to make it clear to President Saddam Hussein that the United States regards the Jan. 15 U.N. deadline for Iraq's withdrawal from Kuwait as the final chance for peace, according to sources familiar with the American preparations for the meeting.

The letter "is pretty direct," spelling out in general the kind of massive attack the international alliance could wage against Iraq and making reference to the advantages of modern weaponry, according to those familiar with the document. It tells Saddam that the survival of his regime would be at stake and although it does not say he would be killed or overthrown, "it comes pretty close to that," one source said.

Baker's overall presentation to Foreign Minister Tariq Aziz is intended to be the culmination of months of pressure on Saddam that has, so far, largely failed to have any impact on him in terms of changing his behavior and forcing him out of Kuwait.

"This is a guy who will go to the brink -- and he may leap beyond it," one well-informed official said of Saddam. "The main danger of a war is that he won't calculate the brink correctly." Thus, Baker hopes to tell Aziz bluntly that the international alliance against Iraq's occupation of Kuwait is not going to keep on waiting and that the Jan. 15 deadline, which comes six days after the Geneva meeting, "defines the brink," as the official put it.

Although Bush and Baker have said the deadline is not one for military action, officials said if there is no Iraqi decision to pull out by then, a separate series of actions could be triggered to prepare for combat.

Baker's brief for the meeting with Aziz in Geneva is also to hold out the promise of survival for Saddam if he capitulates on the main U.N. demands. U.S. officials have left open the question of what kinds of discussions could follow an announced Iraqi pullout. One U.S. official told reporters today, "there would be any number of issues that will still need to be discussed" after an Iraqi withdrawal, including "questions concerning peace and stability in the region."

But the United States has ruled out any direct "linkage" between the gulf crisis and other issues such as Saddam's demands for a resolution of the Palestinian problem. Baker has deliberately left a certain ambiguity about the carrot side of his carrot-and-stick approach to Saddam, even leaving open the possibility of a meeting with the Iraqi leader in a third country.

In the view of American officials, Saddam's reaction to the Baker mission cannot be easily predicted, and thus the prospects for war are mounting. These officials have said for some time that a showdown would come and they now believe the final moments are approaching. They say they are not brimming with optimism that their opponent will suddenly lose his nerve.

After months of frustration trying to build military and political pressure on Saddam, the Bush administration is acutely aware of the difficulty of now delivering a clear-cut message to him amid the cacophony of other voices at home and abroad. Many of these voices, from Congress and from U.S. allies in the anti-Iraq coalition, have been saying that there is more time, perhaps an indefinite period, before the armies in the Arabian desert begin to take the offensive.

"Saddam may miscalculate the brink -- he may be persuaded by watching CNN. He does not understand dissent and the fact we tolerate it may be seen by him as a sign of weakness," the well-informed official said.

The critical date, Baker will tell the Iraqis, is the Jan. 15 deadline. "I don't see any basis for meetings {with Iraq} after the 15th," a senior State Department official told reporters.

These kinds of absolute comments are part of the jockeying for advantage that has been intensifying for months. Although Baker's declaration that the Jan. 15 deadline is the "brink" may be tough talk designed to pressure Saddam into submission, it also may well lock the United States into a course of action from which it would be hard to pull back.

"We have been dealing with this issue for five months. The Security Council gave Iraq and Saddam a 45-day pause for peace," Baker said today after meeting British Foreign Secretary Douglas Hurd here. "We should not be talking about postponing deadlines that we have been saying for five months, or for 45 days certainly, are real deadlines. We have been making the point over and over and over that this deadline is real, and the only real chance we have for peace in my opinion is if Saddam Hussein begins to understand that the deadline is real and we are serious."

Officials said one reason Bush ruled out any visit by Baker to Baghdad was that he realized Saddam could use such a last-minute encounter to undermine the whole concept of a brink beyond which the United States could not go. Officials said they still expect Iraq to try delaying tactics after the meeting with Aziz.

However, they said they hope the letter from Bush will have some impact on Saddam. Baker said today that it "makes it very clear that the question of war or peace is exclusively within Iraq's control."

But the war decision is also one that the alliance would have to make, and part of Baker's discussions this week with coalition partners is how to go about it.

A major part of Baker's trip is to try to muffle the other voices so that his message Wednesday can be heard loud and clear. Starting with his visit with Hurd today, and stops Tuesday in France, Germany and Italy, Baker is trying to create a sound-proof environment for the period from Wednesday until the U.N. deadline six days later.

France has posed particular difficulties because President Francois Mitterrand's peace plan envisions an international conference on Middle East peace issues to follow an Iraqi pullout, which Baker this week rejected as "linkage" to the gulf crisis. Baker sees Mitterrand and French Foreign Minister Roland Dumas in Paris Tuesday.

While France has firmly supported U.N. resolutions against Iraq and deployed troops to the region, it has sought to offer something to Saddam beyond a withdrawal. The American view is that his only reward can be continued survival. "Even the French don't want {Saddam} to get a clear victory," said a U.S. policy maker. "They want him to get something illusory."

The European Community, while rejecting any linkage, has endorsed the Mitterrand approach. Baker today met with Luxembourg Foreign Minister Jacques Poos, current chairman of the EC, in an effort to project a unified front. "We accept no linkage," Poos said. "But, of course, if Iraq leaves Kuwait on the indicated date, there will be an after-crisis discussion."

Baker also met with British Labor Party leader Neil Kinnock, Spanish Foreign Minister Francisco Fernandez Ordonez and NATO Secretary General Manfred Woerner, and in addition to French officials on Tuesday plans to see German Chancellor Helmut Kohl and Foreign Minister Hans-Dietrich Genscher in Bonn and Italian Foreign Minister Gianni De Michelis in Milan.