President Reagan departs today on a 22,299-mile Far Eastern trip that will be dominated by talks with allies about the intensifying threat of Libyan-backed terrorism but is also expected to focus on strained relations with Europe and Japan over trade and economic issues.

The president also plans to discuss his pending decision on whether to abide by the Strategic Arms Limitation Treaty (SALT II) and to review uncertain prospects for a superpower summit this year with Soviet leader Mikhail Gorbachev.

White House officials have dubbed the trip a celebration of the "winds of freedom," emphasizing economic growth and the spread of democracy. But the Reagan odyssey may also highlight differences with allies over use of military force against terrorism.

White House officials have expressed hope that talks on easing trade barriers in Tokyo will deflect congressional pressure for restrictive trade legislation.

Reagan's trip, which is to end May 7, is the longest of his presidency, and he is planning rest stops in Los Angeles and Honolulu. The trip comes amid intensified terrorist actions against the United States and Britain, and officials say special security precautions have been taken.

On his way to the seven-nation summit of industrialized nations , Reagan plans to stop in Bali, Indonesia, for talks with Southeast Asian foreign ministers. For the first time since the fall of Philippine president Ferdinand Marcos, Reagan will consult with a representative of the new government, Vice President and Foreign Minister Salvador Laurel.

Yesterday, Reagan telephoned Marcos' successor, Corazon Aquino, to offer assistance in "meeting the challenges that lie before her government," the White House announced. Reagan told her of his backing for a $150 million package of new economic and military aid, officials said.

Pressure on Reagan to speak to Aquino increased after the White House disclosed that he plans to telephone the deposed Marcos, now living in Hawaii, this weekend during the Honolulu stopover. A senior administration official said recently that Reagan feels badly about what happened to Marcos, whom he considers a personal friend.

The additional $100 million in U.S. economic aid and $50 million in military aid is being gathered through a fund reallocation that must be approved by Congress. In announcing the aid this week, the White House said it is the centerpiece of a "major program" also involving better terms and quicker delivery of previously authorized assistance.

Reagan is to meet with Indonesian President Suharto in Bali and is expected to discuss with the Southeast Asian leaders continued U.S. efforts to resolve missing-in-action cases from the Vietnam war.

First Lady Nancy Reagan is planning a separate trip to Thailand and Malaysia to discuss drug-related issues.

In Tokyo, Reagan is to meet with leaders of Canada, Britain, France, West Germany, Italy and Japan and a representative of the European Community.

A senior U.S. official said that the allies are expected to issue a statement denouncing terrorism and that Reagan will urge further economic actions against Libya's leader, Col. Muammar Qaddafi.

Reagan leaves for the economic summit with U.S. officials boasting of the American economy's performance and heralding it as an example to the other western democracies. In particular, officials say they are looking to Japan and West Germany to take actions to improve growth in their economies as the U.S. expansion tends to moderate.

The unratified SALT II treaty's limits on nuclear missiles will be breached when a new U.S. submarine begins sea trials next month unless two older submarines are taken out of service.

The allied leaders are also expected to compare notes on superpower summitry. Reagan is to talk with French President Francois Mitterrand and Italian Prime Minister Bettino Craxi about their expected meetings soon with Gorbachev, officials said.