British Prime Minister John Major, beginning two days of talks with President Bush, said yesterday the way to avoid war in the Persian Gulf is for Iraqi President Saddam Hussein to withdraw completely from Kuwait.

"The West is serious," the new British leader said. "What he {Saddam} has done is unforgivable and it has to be reversed."

Major's unwavering stance indicated that the resignation last month of Margaret Thatcher, one of Bush's earliest and strongest allies on the gulf, has not weakened British resolve to enforce a United Nations resolution calling for Iraq to leave Kuwait by Jan. 15 or face military action.

Bush and Major are in "full agreement on almost every point" concerning the Persian Gulf situation, including the need to implement the U.N. resolutions, White House spokesman Marlin Fitzwater said last night after the presidential party had motored to Camp David.

The two leaders agree that "partial solutions are unacceptable," Fitzwater said.

Major, the former chancellor of the exchequer and Thatcher's choice to lead the Conservative Party after her, said earlier yesterday that a decision on whether there will be war lies principally in Saddam's hands.

"If he moves back within Iraq, he will not be attacked," Major said. "If he stays within Kuwait, then it is perfectly clear that we may have to expel him forcibly."

Major said he was "sad" that Soviet Foreign Minister Eduard Shevardnadze had resigned suddenly, calling the Soviet official "a remarkable peacemaker" over the past few years. He added he was encouraged by Soviet President Mikhail Gorbachev's statements that the resignation would not change Soviet foreign policy, but said part of that could depend on who replaced Shevardnadze.

Secretary of State James A. Baker III, emerging from a session with Major, sounded a pessimistic note about prospects for peace in the gulf. "So far at least, the behavior of the governor of Iraq, in the aftermath of these United Nations resolutions, would not make one optimistic that we could succeed in our very strong effort to achieve a political, peaceful resolution."

National security adviser Brent Scowcroft told wire service reporters yesterday that while Jan. 15 "is not an attack day," the Iraqi leader puts himself at risk from that day on, if he has not pulled out his troops.

Major said a partial withdrawal from Kuwait, which some U.S. officials fear Saddam might be contemplating, cannot be tolerated. "A partial pullout will not do," Major said. "He has to go and go completely."

Baker, who said he is still prepared to go to Baghdad to meet with Saddam, repeated the administration's assertion that talks with Iraq will not be used to negotiate concessions.

"Nobody that I know of is willing to negotiate backwards from the United Nations Security Council resolutions," Baker said. "If we do that, we would be repeating the same mistakes that the world made in the Thirties, when we appeased aggression. We simply cannot appease aggression."

Major called Iraq's invasion and continuing occupation of Kuwait "a unilateral piece of nastiness" that cannot be dealt with through negotiations or concessions. "He really has to get out," Major said. "There's no compromise on that point. If there's not to be a conflict, it is in Saddam Hussein's hands."

Major spent a busy day yesterday that began with TV interviews and included meetings with Baker, Vice President Quayle, Treasury Secretary Nicholas F. Brady, Federal Reserve Board Chairman Alan Greenspan, and congressional leaders.

Major and Bush will hold a news conference today at Camp David, shortly before Major departs.

Bush met yesterday at the White House with ambassadors from Saudi Arabia, Kuwait and some other nations that have contributed financially to the Persian Gulf effort.