HELSINKI, SEPT. 8 -- President Bush and Soviet President Mikhail Gorbachev arrived here today for their meeting Sunday, stressing from different perspectives the importance of continued superpower cooperation in responding to Iraqi President Saddam Hussein's aggression in the Persian Gulf.

An expansive Bush said he hoped the informal, one-day talks would "strengthen our common approach" against Saddam, adding that the result of this cooperation could be a safe, more secure world.

"If the nations of the world, acting together, continue as they have been to isolate Iraq and deny Saddam the fruits of aggression, we will set in place the cornerstone of an international order, more peaceful, stable and secure than any that we have known," he said at an arrival ceremony this morning.

A more subdued Gorbachev, facing massive economic problems at home, arrived early this evening with a similar message, although he couched it in terms of the challenges he confronts in the Soviet Union. The talks, he said, occur at a "crucial moment in history when it is very important to compare our political approaches and to cooperate in order to protect the positive trends evolving in the world today, to make sure they are not thwarted by any development."

Bush and Gorbachev, who did not see each other today, are expected to find much to agree on here when they meet Sunday. The U.S. president has offered continued support for Gorbachev's reforms at home. The two leaders also have agreed thus far on sanctions against Iraq, and U.S. officials are expecting to get further cooperation in the gulf from the Soviet leader, especially on the enforcement of the sanctions.

But the use of military power if those sanctions fail could produce differences between the two leaders. Bush is expected to use the summit to explore the range of options that might be considered if the crisis drags on indefinitely. Gorbachev has been chilly to the idea of military action, preferring to see a diplomatic solution.

The meeting here was hastily arranged, at Bush's request, and it was not clear whether there also was some secret agenda of U.S. plans that the American president wanted to lay out for Gorbachev.

A senior administration official said that while he expects the Soviets to show solidarity with the United States, there are limits to what the Soviets will do. "I expect a good meeting," he said. "I think they're going to be cooperative. I don't think they'll give us a blank check."

On the eve of the third meeting between the two leaders, Iraq's Saddam sought to stir division with a statement read over Iraqi television by his spokesman. Saddam warned Gorbachev that "there are doubts in the world about the place of the Soviet Union as a superpower" and said the United States was seeking to become the "sole power" through its military deployment in the gulf.

U.S. officials brushed aside the rambling statement from the Iraqi leader, saying they would have no reaction and that Bush wanted only cooperation with the Soviets.

Bush appeared exuberant when he arrived here today after an eight-hour flight from Washington aboard his new Boeing 747 Air Force One. Stealing a leaf from Gorbachev's travel book, Bush stopped his limousine, under a gray, chilly sky, and plunged into a crowd near an open air food and vegetable market. As he climbed back into his limousine after shaking hands on the streets of Helsinki, Bush exclaimed over the automobile's loudspeaker: "Thanks very much. Long live Finland!"

Thousands of people lined the streets of Helsinki as Bush's motorcade made its way from the Helsinki-Vantas Airport to the Presidential Palace in the center of town, where Bush met with Finnish President Mauno Koivisto.

Bush and Gorbachev will discuss a wide range of issues related to the gulf crisis, but the focus of administration officials remained on winning Gorbachev's continued strong support for the international effort to squeeze Iraq with economic sanctions in the hope that it will force Saddam to withdraw his forces from Kuwait.

U.S. officials believe that this public display of superpower unity, taking advantage of the considerable international prestige that Gorbachev brings to the situation, will be the most powerful signal to date that Saddam is now isolated, demonstrate that there is no erosion in the commitment to enforce the sanctions against Iraq and help Bush sustain the diplomatic and military pressure on the Iraqi leader.

Bush made clear how crucial continued Soviet support is when he told the staff at the U.S. Embassy: "If you wanted to think of a complicated situation, shift the clock back several years and think about how difficult it would be to work this equation now, get the international support that has been gotten, but try to do it without the Soviet Union being a part of it."

But while unity was the theme for the weekend, Bush and Gorbachev will find a number of potential differences to discuss during their two meetings and lunch on Sunday. These include the continued presence of nearly 200 Soviet military advisers in Iraq, an irritant that the United States would like to see removed. It was not clear whether Gorbachev was ready to agree to the administration's request.

Bush also may encourage greater Soviet participation in the military effort in the gulf region, but he told reporters that he has "no plans" to ask the Soviet leader for ground forces there.

Administration officials said Bush wants to show support for Gorbachev at a time of trouble for the Soviet leader back home.

While he is expected to maintain support for the U.S.-led response to Saddam, Gorbachev is expected to seek reassurances that the United States will not initiate military hostilities against Iraq and that economic sanctions and diplomacy be used to resolve the crisis. On Friday, Soviet Foreign Minister Eduard Shevardnadze said he was "ready if necessary" to go to Iraq to explore a peaceful solution to the crisis.

While Bush has said he does not see a mediating role for the Soviets, White House chief of staff John Sununu indicated on Cable News Network today that the United States might like the Soviets to continue to deal directly with Baghdad.

Gorbachev is expected to advance Soviet proposals for an international conference on the Middle East and a greater United Nations role in overseeing the military effort there.

Bilateral issues also will play a role in the talks, including economic aid to the Soviet Union. En route to Helsinki, Bush said he was "all for" an exchange in which the United States would provide technical support to the Soviets to produce more oil in return for a share of that oil.

Bush also said today he would talk to Gorbachev about the continuing changes in Europe, adding that he sought "to advance the pace of arms control, strategic and conventional."

Bush and Gorbachev will meet at the Presidential Palace at 10 a.m. That 2 1/2-hour meeting will be followed by a lunch hosted by Koivisto for Bush, Gorbachev and their wives. The two leaders will meet for 2 1/2 hours in the afternoon. At 5:30 p.m., they will hold a press conference.