The United States and the Soviet Union closed ranks yesterday as the Soviet leadership rejected Iraqi conditions for a pullout from Kuwait and President Bush expressed confidence that the Kremlin would not compromise in a new round of high-level diplomacy with Iraq.

As Iraqi Foreign Minister Tariq Aziz prepared to leave for talks with Soviet President Mikhail Gorbachev planned for Monday, Bush said he had received "very fresh" assurances that the Soviet leadership would stand firm against any departure from United Nations resolutions calling for the unconditional withdrawal of Iraqi forces from Kuwait. Gorbachev has been "very solid" and played a "constructive role," Bush told reporters in Kennebunkport, Maine, where the president is spending the weekend.

Soviet Foreign Ministry spokesman Vitaly Churkin told a news conference in Moscow that Iraq's statement Friday indicating a willingness to pull out of Kuwait under numerous conditions was not acceptable to the Soviet leadership, but might be an "initial step" toward a diplomatic solution. Churkin added that Soviet leaders would use the Aziz visit to explore Baghdad's intentions in greater detail.

Gorbachev, speaking to a delegation of European Community foreign ministers, said yesterday it was "never too late" to make "maximum use of diplomatic-political methods" to end the Persian Gulf War. The Soviet leader sent Bush a letter Thursday, U.S. officials said, outlining his hopes for the Aziz meeting and asking that any allied ground offensive be delayed until after the Iraqi minister's visit. Alliance officials said yesterday that no major ground offensive had been imminent anyway.

Notwithstanding Bush's outward expression of confidence, senior U.S. policy-makers are watching the diplomacy in Moscow with intense interest. They expect it to be a critical test of whether Iraq is serious about leaving Kuwait and also a challenge to Gorbachev, who is under pressure both from Soviet hard-liners sympathetic to Iraq and from international coalition members committed to the U.N. resolutions against Iraq.

Allied forces continued yesterday to prosecute the war from the air, flying another 2,600 sorties, many aimed at Iraqi armor, supply lines and communications facilities, U.S. military officials reported. Defense Secretary Richard B. Cheney said in a television interview that "we don't believe there's any room here for any pause, any cease-fire, or anything other than complete, total, unconditional compliance with the U.N. resolutions." Cheney said any such pause would give Iraqi President Saddam Hussein "time to repair some of the damage, to redeploy his forces" and that this could cost American lives.

U.S. Army Apache AH-64 attack helicopters, artillery and multiple-launcher rocket systems joined in a combined nighttime attack on Iraqi forces. It was the first time Apache helicopters have been used in such operations and represented some of the tactics expected in a ground offensive, if one becomes necessary.

Iraqi antiaircraft gunners shot down two U.S. A-10 Thunderbolt warplanes on night bombing missions against Republican Guard units in northwestern Kuwait. The pilots of both aircraft were listed as missing in action.

Iraq fired two Scud missiles at Israel, hitting the southern part of the country for the first time. No injuries or damage was reported.

Iraqi authorities claimed that 130 civilians were killed by allied bombs that demolished an apartment building and market in the town of Fallujah, about 40 miles west of Baghdad. Reporters were escorted to the town to inspect the scene of the damage, and they quoted Iraqi officials as saying that warplanes aiming for two strategic bridges demolished one but also hit the building and market. In London, British officials said Tornado warplanes had been attacking bridges in the area but said there was no evidence the raids occurred at the same time as the apartment building was destroyed. Baghdad 'Faking' Damage

In Washington, Navy Rear Adm. Mike McConnell accused Iraqi authorities of contriving some of the bomb damage in Iraq displayed recently to reporters. "Yes, they are faking some of it," he told a Pentagon briefing. He accused Baghdad authorities of causing "collateral" damage to at least one building and then parading Western news media in front of it for propaganda purposes.

He did not specify the building, but another U.S. official said a mosque near Basra may actually have been dismantled by Iraq. Satellite photographs of the mosque showed the dome missing but window casings intact, an absence of debris on lower floors and walls that had been detached but were not buckled as they would have been from bombing, according to the official.

Allied officials also pressed their claim that Saddam has mingled his war machine with civilians to protect it. British Air Chief Marshal Patrick Hine told reporters in Riyadh: "There are a large number of aircraft parked around one of his main bases in residential areas. There is a brigade headquarters parked immediately beside a school. There is a whole line of heavy-duty fuel tankers parked in the middle of a cemetery. And there is another photograph I have seen of military headquarters and combat vehicles parked in and around a hospital."

Cheney, appearing on Cable News Network's "Newsmaker Saturday" broadcast, suggested that the bombed structure in Baghdad in which civilians were killed last week may have been reserved for families of the elite. The shelters in Baghdad could accommodate "a maximum of maybe 1 percent" of Baghdad's 4 million residents, he said. "It's not the kind of thing that you ordinarily would have passed out to the average man on the street," he said. Ground War Not Imminent

Allied military leaders indicated yesterday that the start of a major ground offensive may still be some days away. Hine said two criteria must be met before the attack is launched: Allied forces have to be "fully prepared in their forward positions and properly supported logistically," and commanders must be "confident that the interdiction and attrition process has reached the point" where the ground campaign can be launched "without the risk of heavy loss of allied lives."

Hine said the planned ground campaign had not been accelerated "because of any political factors" such as Iraq's diplomatic initiative.

The Pentagon yesterday released revised figures for the amount of Iraqi armor destroyed in Kuwait and southern Iraq, showing a small increase since numbers given Thursday: 1,400 out of 4,280 tanks; 1,200 out of 3,110 artillery pieces; and 800 out of 2,870 armored personnel carriers.

About 523,000 U.S. military personnel are now deployed in the region, Lt. Gen. Thomas Kelly, operations director for the Joint Chiefs of Staff, said yesterday. The figure represented an increase of roughly 17,770 within the past week.

Iraq's ambassador to the United Nations called yesterday for negotiations on the basis of Baghdad's Friday initiative, and criticized the abrupt U.S. dismissal of the proposal. Ambassador Abdul Amir Anbari said that "over the past few weeks we have heard so many complaints that Iraq simply would not utter the word 'withdrawal' or utter the word 'Kuwait,' " he said. "Now, when Iraq came with this important proposal . . . they said our list is just a piece of propaganda."

In its statement Friday, Iraq's Revolutionary Command Council indicated a willingness to comply with the first of a series of U.N. Security Council resolutions passed last year demanding an Iraqi withdrawal, but stated a number of conditions. The conditions included, among others, Israel's withdrawal from the West Bank, Gaza Strip, Golan Heights and southern Lebanon; evacuation of all foreign forces from the gulf; payment of reparations to Baghdad; and cancellation of other U.N. resolutions imposing sanctions on Iraq. Initiative Interests French

Sources said the Iraqi initiative has intrigued senior French officials largely because of accompanying signals that they have just received from Baghdad, Moscow and North Africa. Well-informed French sources said there are reports that high-ranking Iraqis, primarily in the military, contend the country should now retreat from Kuwait after having held fast against one month of intense bombardment. The argument of this faction, French sources said, is that Saddam and the country are better off pulling back now while there is still a chance to salvage parts of the military and industrial infrastructure and reap political rewards for having resisted the overwhelming air assaults.

That notion would augur well for the talks in Moscow this weekend. But the French sources said they have also learned that Iraqi Deputy Prime Minister Saadoun Hammadi, during a tour of North African states last week, told his hosts that real negotiations on ending the war would only commence three weeks after the ground war had started and that the Americans may have suffered as many as 6,000 deaths. Hammadi, who despite his senior position is not thought to be part of Saddam's inner circle, also insisted during his visits to Tunisia, Algeria and Morocco that the war has been proceeding exactly as the Iraqi leadership expected.

Staff writers R. Jeffrey Smith, William Drozdiak in Paris and Jackson Diehl in Jerusalem, and researcher Ralph Gaillard Jr. contributed to this report. Balz reported from Kennebunkport, Hoffman from Washington.