Leaders of 22 nations arrived today for an unprecedented two-day summit conference starting Thursday on how to reduce hunger and poverty in the developing world of the "South."

There were hints that President Reagan and other heads of the industrial "North" countries were anxious for a positive, if limited, result. While a spirit of compromise was evident as well among some influential delegations from the South, there also were clear indications that many of them will be pressing for decisions that may prove hard to make for leaders from developed countries.

Reagan held several bilateral meetings today, including his initial contact with China's leadership in a session with Premier Zhao Ziyang that reportedly touched on the Taiwan issue as well the Cancun summit.

A senior U.S. official said late today that "everyone is hopeful that this will be a successful meeting, and I am optimistic that it will be." The simple fact that there is a summit "is in itself an evidence of success," he said.

The official insisted that the U.S. approach is flexible, saying the sort of compromise the Reagan administration hopes will come out of Cancun "is a combination of the proper investment climate for free interprise, improved trade relationships . . . and help, call it aid, for the needy world. We're not looking for a redistribution of assets, but creating the circumstances that can permit economic growth."

He added that if a consensus develops among the 22 nations along these lines, it could be followed up in "bilateral or multilateral fora -- it would then be a success."

Reagan, on departure from Washington this morning, said that by participating in the Cancun summit, the United States is fulfilling "a commitment" to a stronger world economy, a commitment that is a "top priority of American foreign policy." Reagan's willingness to come here contrasts with former president Carter's refusal to engage in a North-South dialogue.

"But we go to Cancun with no illusions," Reagan said. "The problems of hunger and poverty are severe and deeply rooted. They cannot be solved overnight, nor can massive transfers of wealth somehow miraculously produce new well-being."

Reagan earlier said he expected "a hostile environment" in Cancun. But he emphasized today that "with cooperation and good will, this summit can be more than just another shattered dream."

At the airport here, Reagan embraced summit cochairman, Mexican President Jose Lopez Portillo, who spent the day welcoming his distinguished visitors. Arrivals were scheduled 30 minutes apart except for a one-hour gap after Reagan's arrival to allow for a 30-minute bilateral U.S.-Mexican meeting in the airport lounge.

Lopez Portillo, dressed informally in white trousers and a flowing white shirt on a hot, windy day, seemed to be bearing up well. The Mexican band on hand to play the Mexican national anthem and the guest's national anthem for each arrival seemed to step up its tempo as the day wore on through 90-degree heat.

The welcoming ceremonies included ear-splitting 21-gun salutes from a line of howitzers. After each guest left for the Cancun Sheraton Hotel, Lopez Portillo ducked into the air-conditioned lounge for a quick breather.

In spite of Reagan's implied hope for positive achievement out of Cancun, there were hints that the Third World nations have no intention of succumbing to the president's well-known charm, certainly not to the point of abandoning efforts to enter "global negotiations" with the rich nations for a more significant share of the world's wealth.

The Third World nations prefer such negotiations under the aegis of the United Nations, where they hold a majority. Having studied Reagan's recent speeches in Philadelphia and to the annual meetings of the International Monetary Fund and World Bank, they are prepared for the president's pitch for reliance on the private sector. But they plan to say that is not enough.

Sources close to the Chinese delegation indicated that it will strongly support the demand for global negotiations. Zhao, in his first appearance on the international debating scene, was said to be anxious to demonstrate that China lines up ideologically with other Third World nations.

Similar intimations that some delegations will insist on negotiations in the United Nations -- a proposal always strongly resisted by the United States -- came from Nigeria and other Third World countries.

Yet a desire to avoid confrontation was evident in comments by Philippine President Ferdinand Marcos and others. On arrival, Marcos suggested to his Third World compatriots should be less demanding and should put aside their bitterness of the past.

"Poking into the debris and dregs of the past is not the way to discover our future," Marcos said.

This theme was echoed as well by Austrian Foreign Minister Willibald Pahr, filling in for ill Chancellor Bruno Kreisky, who was to have been cochairman with Lopez Portillo. A new cochairman has not yet been designated, but in all likelihood it will be Canadian Prime Minister Pierre Elliott Trudeau.

In explaining the British position on two major areas of discussion in the summit, Lord Carrington, the British foreign secretary, said his government "supports the creation of an energy affiliate of the World Bank... and global negotiations in whatever form is useful."

His previous comment on the same subject had been noncommittal. The United States has opposed creation of a separate fund within the World Bank to finance lending to underdeveloped countries for energy. It also has rejected in general the concept of "global negotiations," which has become a catch phrase for the Third World in its pursuit of the restructuring of the international economic order.

"Global negotiations," Carrington said, "are defined by different people in different ways. I define them as global problems that have to be settled in the United Nations. I think the most useful thing here would be to state clearly what we do mean by global negotiations."

The British position on global negotiations and the energy affiliate would seem to leave the U.S. almost totally isolated on these positions, with the possible exception of Japan. But a senior administration spokesman said tonight that President Reagan would state the current U.S. position on the critical issue of global negotiations tomorrow.

He turned aside the suggestion that the United States would back away completely from its opposition to global negotiations, but said: "A dynamic process is under way, broadening the viewpoints of both sides."

The official emphasized again that after additional bilateral meetings that now have put Reagan in touch with nearly a half-dozen of the poor countries, "I am increasingly comfortable that there is a consensus, and that we will achieve a consensus in some important areas."

On the question of private investment and the lowering of trade barriers instead of an increase in foreign aid as a means of aiding the Third World -- the position of the United States -- Carrington again put Britain at some distance from Washington. "My government's view is that aid is essential to the poorest countries in the world," he said, adding that since income from trade for the developing world is about 20 times that of foreign aid, "we should also support it."

In addition to bilateral meetings with Mexico and China, Reagan held sessions today with Prime Minister Indira Gandhi of India and Presidents Luis Herrera Campins of Venezuela and Shehu Shagari of Nigeria. Reagan plans sessions Thursday with leaders of Yugoslavia and the Philippines, and on Friday and Saturday with those of Bangladesh, Guyana, Saudi Arabia and others.

In a briefing following the Reagan-Lopez Portillo meeting, a Mexican spokesman said Lopez Portillo emphasized his country's belief that although the success of the meeting is a responsibility divided among all attending countries, "the greatest responsibility...rests with the developed countries."

The Mexican said Reagan expressed a willingness to listen to various positions and that the United States would act with "flexibility."

Reagan, the Mexican said, opted for freer trade and said he hoped that the rest of the countries of the developed world could have policies similar to those of the United States, although, the spokesman added, Reagan "admitted that the United States might have to do even more to open its markets to the exports of underdeveloped countries."

The senior U.S. official who briefed reporters said Reagan's meeting with Chinese Premier Zhao was "very important" in the developing relations between the two countries and had dealt with the Chinese relationship to Taiwan as well as with the basic issues here.

The official said that in Reagan's first meeting with Gandhi, the two leaders noted that India's "great success" with the "green revolution" in agriculture "closely parallels Reagan's own views" on the way economic growth can be enhanced within poor countries. This involves the transfer of "technology, skill and knowledge," not a mere transfer of financial resources.

Also contributing to this story were Karen DeYoung and Lee Lescaze of the Washington Post staff.