Embarking on his Moscow summit journey Wednesday, President Reagan told a gala farewell gathering that despite "deep differences, moral differences" the United States and the Soviet Union can work together for peace.

Expecting no arms control breakthroughs in his fourth meeting with Soviet leader Mikhail Gorbachev - and not even sure of having a finalized INF missile treaty in time for the summit - Reagan focused on the long-term outlook for East-West relations.Some 1,500 dignitaries, including the Cabinet and members of the diplomatic corps were invited to the send-off where Reagan made a statement on the South Lawn of the White House setting forth his goals for the summit.

"I do not expect it to be easy," Reagan said. "We have many differences - deep differences, moral differences. But we are still fellow human beings, we can still work together to keep the peace. And in working with the Soviet Union, the United States can still remain true to its mission of expanding liberty throughout the world."

While concerned that the Senate may not approve the INF treaty by the time he arrives in Moscow Sunday, the president, looking toward future accords, noted progress in negotiations on a Strategic Arms Reduction Treaty.

The INF treaty would eliminate all land-based nuclear missiles with ranges of 300 to 3,400 miles, and START would provide for a 50 percent slash in long-range nuclear arsenals.

"In my talks with General Secretary Gorbachev next week, we will be looking to the future for there remains much to be done."

On regional conflicts, he said the United States will be looking for Soviet actions to help advance negotiations on Angola and Namibia and to support U.N. efforts to end the Iran-Iraq War.

He said the Soviets also would be urged to use their influence with the Ethiopian government to prevent a massive "man-made crisis of starvation there."

Further, he invited the Soviets to help move the Middle East peace process toward some useful exchanges."

White House spokesman Marlin Fitzwater described his boss as "optimistic" for some measure of benefit from the Moscow visit May 29 to

June 2, which includes five meetings with Gorbachev and a solid dose of image crafting on both sides.

Reagan's first stop on the 10-day, 10,705-mile journey is Helsinki, Finland, where he and his wife, Nancy, will have a low-key stay, highlighted by one major address at Finlandia Hall featured as a prelude to the summit.

While it is mainly a rest stop, the presidential party is expected to spread out in Helsinki to meet with Soviet Jewish groups holding a conference in the Finnish capital. Reagan will conclude his trip with an overnight stop in London to talk with Queen Elizabeth and Prime Minister Margaret Thatcher.

The president was generally exuberant on the eve of Wednesday's sendoff, subdued primarily by concern that the Senate had not yet ratified the Intermediate Nuclear Forces Treaty he signed with Gorbachev in Washington Dec. 8.

Reagan failed to persuade a band of archconservative GOP senators to stop delaying the treaty Tuesday, and he decided to leave White House chief of staff Howard Baker behind to monitor Senate action in the hope that Baker would be able to fly to Moscow this weekend with a ratified treaty.

Otherwise the president tried to clear the decks, touching all advisory bases in meetings with his Cabinet, the Foreign Intelligence Advisory Committee and congressional leaders of both parties.

Secretary of State George Shultz announced to wire service reporters that the United States would bring to Moscow new verification proposals covering mobile land-based ballistic missiles, one of the major issues standing in the way of a U.S.-Soviet agreement reducing long-range strategic nuclear weapons.

"Verification is harder with mobile missiles than with stationary ones, for obvious reasons, but there are ways of coping with the problem, we think. We will make our proposals," Shultz said.

U.S. officials have cautioned there will be no big breakthroughs on the arms control front. Assistant Secretary of State Rozanne Ridgway said human rights will be at the top of the agenda.