Soviet leader Mikhail Gorbachev arrived in Washington late yesterday hailing the treaty eliminating U.S. and Soviet medium-range and shorter-range nuclear missiles to be signed at the White House today, and called for "some new words" from President Reagan in their summit talks ahead on the more far-reaching accord to slash long-range nuclear arsenals.

As dusk fell at Andrews Air Force Base, the general secretary of the Soviet Communist Party, accompanied by his wife, Raisa, landed after a flight from Moscow with a refueling stop in England, for a red-carpet reception marking his third summit meeting with Reagan and the first U.S.-Soviet summit in 14 years on U.S. soil.

"On behalf of the people and the government of the Soviet Union, I want to assure all Americans that we are sincerely striving to improve our relations," said Gorbachev in a brief, businesslike and hopeful statement.

Gorbachev, 56, wearing a dark suit and overcoat, fedora and eyeglasses, stood before a microphone on the chilly tarmac, speaking in Russian in confident tones, without notes. His wife, wearing a knee-length silver-fur coat, stood quietly beside him, holding several bouquets of flowers presented at their arrival.

Gorbachev declared that the heart of his discussions with Reagan and "the central question of Soviet-American relations" is the negotiations to reduce the strategic nuclear missiles and bombs that have piled up in vast numbers in the 40 years of cold war hostility.

"We have something to say to the American leaders on that main question," he declared, seeming to hint that he was bringing some of the diplomatic surprises for which he has become known, especially since last October's high-stakes summit at Reykjavik, Iceland. "And we are hoping that we will hear some new words from our partners."

Despite repeated U.S. declarations that the arms treaty was complete, a hitch developed late yesterday when the United States rejected a Soviet photo of an SS20 mobile missile, a weapon to be eliminated under the treaty.

State Department spokesman Charles E. Redman said the photo "is not satisfactory," and that "we assume" a satisfactory replacement will be supplied.

Informed sources said U.S. intelligence has never obtained a clear SS20 photo, crucial to verify that the weapons have been dismantled or destroyed, as the treaty requires.

The disputed Soviet photo reportedly shows the protective container used to transport an SS20, not the actual missile. The dispute had not been resolved by late last night, even though it had been hours since Gorbachev's arrival and Reagan's response.

Reagan reserved his expression of hope for the summit for the official welcoming ceremony this morning, but during the lighting of the national Christmas tree last night, he said that if Gorbachev was watching, "I'd like him to see what we're celebrating because, for us, Christmas celebrates the cause of peace on earth, good will toward men." Earlier in the day White House spokesman Marlin Fitzwater said that "the president approaches this summit with a sense of realism, a sense of promise, and a belief that dialogue is essential in the quest for peace."

The summit begins this morning with a formal White House ceremony, including full military honors, at which Gorbachev will be welcomed by a president whose early years in office were characterized by harsh anti-Soviet rhetoric and the biggest peacetime military buildup in U.S. history.

A 90-minute morning business session is to follow, in which the two leaders are expected to broadly discuss U.S.-Soviet relations. After a break, Reagan and Gorbachev are scheduled to sign the intermediate-range nuclear forces (INF) treaty in the East Room at 1:45 p.m. Each leader will address the signing ceremony and then broadcast brief statements to the Soviet and American peoples from the State Dining Room. Then they will return to the work of their negotiations.

Gorbachev's initial remarks after alighting from his special four-jet Ilyushin-62 Aeroflot airliner, along with the statements of U.S. and Soviet spokesmen earlier in the day, established an atmosphere of expectation and optimism about the three days of meetings ahead.

"The visit has begun . . . . So let's hope," said Gorbachev to Secretary of State George P. Shultz as he finished his arrival statement, adding, "May God help us."

"We are ready," Shultz responded.

"You know, we are ready too. We will see that tomorrow," said Gorbachev.

The Soviet Union is officially an atheist state, but its leaders have referred to God on numerous occasions. The late Leonid Brezhnev did so when meeting President Jimmy Carter in Vienna in June 1979, and Gorbachev spoke of God in a 1985 interview with Time magazine.

Subsequently Reagan remarked on Gorbachev's allusion to the Deity, saying, "I have to believe that if he is talking to God, we ought to get along, because so am I."

The Andrews arrival ceremony lasted about 15 minutes, then the Gorbachevs and their entourage climbed into sleek black Zil limousines that had been flown here in the past week. Their motorcade, accompanied by a heavy uniformed police and plainclothes escort, sped along the Suitland Parkway into Washington.

They drove directly to the heavily guarded, barricaded embassy on 16th Street NW, a few blocks north of the White House, where they are to stay during the visit.

Forty minutes after Gorbachev landed, a U.S. Air Force plane from Geneva landed at the same runway, bringing members of the U.S. and Soviet teams that negotiated the INF treaty in six years of painstaking and sometimes tortuous bargaining, which was punctuated by a 16-month Soviet walkout.

Maynard W. Glitman, head of the U.S. team that completed the INF negotiations, carried the 150-page text of the treaty in his briefcase. With him and about 30 other members of the U.S. team were Soviet INF negotiators Alexei Obukhov and Gen. Vladimir Medvedev.

At a picture-taking ceremony before a final preparatory meeting with the Joint Chiefs of Staff yesterday, Reagan strongly defended the INF accord, which has been criticized by some conservative senators and opposed by four of the six Republican presidential candidates.

Delivering what he said were "opening remarks" to the Joint Chiefs, Reagan called the treaty the "highlight" of the summit. He reminded the accord's critics that he has always said he'd rather have no treaty at all rather than one that did not enhance the security of the United States and its allies.

"The INF treaty meets that test," Reagan continued. "It's a solid accomplishment for the United States and our allies, and for the first time we will reduce nuclear weapons, rather than just limit their building . . . .

"We've done this without weakening the other elements of our defensive posture in Europe, and we'll have the toughest verification provisions of any treaty on the books."

U.S. officials said the treaty will require dismantling 859 medium-range and shorter-range U.S. missiles and 1,941 comparable Soviet missiles, many with three warheads.

The Joint Chiefs formally endorsed the treaty at their meeting with the president, according to a U.S. official who declined to be identified. Reagan was criticized after his Reykjavik summit last year because he negotiated on sweeping nuclear arms cuts that would have affected U.S. security without first consulting the military service heads.

According to a U.S. official familiar with the discussions at yesterday's meeting, the chiefs also urged Reagan to press Gorbachev to support a U.S.-initiated drive to impose a U.N. arms embargo against Iran for its actions in the Iran-Iraq war.

Meanwhile, a move developed in the Senate Foreign Relations Committee to rescue a Capitol Hill meeting with Gorbachev. An earlier plan for the Soviet leader to address a joint meeting of Congress was scrapped after conservative Republicans in the House angrily objected.

Foreign Relations Committee Chairman Claiborne Pell (D-R.I.) wrote Gorbachev last week, inviting him during his visit to meet with panel members, Senate leaders and senior members of the Armed Services and Intelligence committees, all of whom are expected to play major roles in the debate over ratification of the treaty.

After the GOP revolt derailed the proposed Gorbachev address to Congress, lawmakers were told that he was determined not to come to Capitol Hill but would meet congressional leaders only on his own embassy turf. However, a Foreign Relations Committee source said he understood Pell's invitation is under "active consideration" by the Soviets.

The meeting would be held in the Foreign Relations Committee room in the Capitol, where a similar meeting was held for former Soviet leader Nikita Khrushchev during his visit to the United States in 1959.

But Senate Minority Leader Robert J. Dole (R-Kan.), who is expected to be a key figure in the ratification debate, called for a cooling of "glasnost fever" in a speech to a closed-door meeting of Gannett newspaper executives. Dole contended that the INF treaty has strained the Atlantic alliance, and he urged a go-slow approach to a Moscow summit.

"Let it happen when arms control events, and not our political calendar, dictates," he said.

Dole is one of nine congressional leaders scheduled to meet with Gorbachev at the Soviet Embassy on Wednesday morning. Another participant, House Speaker Jim Wright (D-Tex.), said he planned to bring up "the whole range of things that make up our relationship," including human rights and regional issues.

Many of these issues came up yesterday at an unusual dual news conference by U.S. and Soviet spokesmen at the newly opened summit press center at the J.W. Marriott Hotel, where briefings will be held for more than 7,000 journalists and technicians from around the world accredited to cover the event.

Fitzwater and Soviet Foreign Ministry spokesman Gennadi Gerasimov shared the podium side by side, exchanging one-liners and parrying questions from reporters.

Gerasimov was asked if he thought Sunday's rally of 200,000 here in support of liberalized Jewish emigration from the Soviet Union was an "officially inspired anti-Soviet" demonstration or a genuine expression of American public opinion.

"I don't think it was an anti-Soviet demonstration, as you put it," Gerasimov replied. "It was a demonstration on one issue . . . . Jewish emigration . . . . Those who took part in this demonstration wanted to make the point, and I think they did."

Gerasimov was also asked "how many more Afghans do you have to kill" before the Soviets withdraw the reported 115,000 troops they have in Afghanistan. He replied calmly that the Soviets had made "a political decision" to withdraw and that this would be discussed at the summit.

One feature of the briefing, and of an earlier Cable News Network interview with White House chief of staff Howard H. Baker Jr., was an effort to separate a Reagan trip to Moscow next year from a requirement that a strategic arms agreement be ready for signing at that time.

Baker said a Moscow summit next May or June "is a strong possibility" and that the successful negotiation of a strategic arms treaty, in his view, is not "a necessary pre-condition." Referring to the strategic arms reduction treaty, Fitzwater said, "We will be working toward the START treaty in the months ahead, but we would not necessarily link" it with a Moscow summit.

When they announced the Washington summit Oct. 30, the two nations said in a joint statement they would work toward early agreement on a treaty reducing strategic nuclear arms by 50 percent, "which could be signed during the president's visit to Moscow."

A White House official said at the time that an agreement on strategic arms is "effectively linked" to Reagan's Moscow trip. Soviet Foreign Minister Eduard Shevardnadze said at a news conference that day that "the main result of that {Moscow} visit and we understand that the U.S. administration agrees would be the signing of the treaty on the 50 percent reduction of strategic offensive arms."

A White House official said yesterday that "in everybody's mind the {strategic arms} agreement and the Moscow summit are effectively linked, but we don't want to get bogged down in that in public statements." He added, "We also want to be in the position of keeping our options open, in case there is a reason to go to Moscow and an agreement isn't ready to be signed."

Shultz, who with his wife had tea with the Gorbachevs at the Soviet Embassy after their arrival, followed up with a 50-minute meeting at the State Department last night with Shevardnadze on final preparations for the leaders' face-to-face meetings. "Everything is fine," Shevardnadze said as he left.

Staff writers David Hoffman and Helen Dewar and staff researcher Michelle Hall contributed to this report.