A multicultural, polynational madness has settled over this resort as delegations from 22 nations arrived today, and began getting acquainted and vying for attention in anticipation of the North-South summit starting Thursday.

Philippine President Ferdinand Marcos, for instance, despite what looks like half the Mexican Navy floating outside the Sheraton Hotel to protect its stellar occupants from seaborne attack, decided this morning to spend 45 minutes water skiing.

With a security helicopter flying overhead and a camera crew filming his every turn, Marcos swooped across the lagoon before finally doffing his wet suit and granting an interview to reporters from National Public Radio, who, like much of the press here, were starved for any hint of hard news to break the deluge of presummit platitudes.

Just to make sure no one forgets him in the crush of dignitaries, Marcos has distributed biographies of himself to 2,000 reporters.

Other leaders launched immediately into a series of bilateral meetings, luncheons and dinners, jockeying for firm positions before the general dialogue begins Thursday morning. But such hints of content as emerged from these encounters tended toward minuscule points of protocol.

Rumors abound, for example, that the People's Republic of China will take a tough line with the Reagan administration on questions of U.S. aid to the developing world, with Peking wanting to appear as the champion of the South. The relatively small contingent of Chinese journalists was almost mobbed by other reporters anxious for some solid indication of Peking's thinking.

Chinese Premier Zhao Ziyang, meanwhile, arrived 15 minutes late for lunch with Reagan, so the American president instantly seized the opportunity to be gracious by noting that such tardiness is common in Latin America.

Shortly thereafter, at another meeting, Indian Prime Minister Indira Gandhi said rather pointedly that while all the suites at the Sheraton are supposed to be equal, Reagan's is two floors above her.

"Yes, and it's a beautiful view," responded the president.

Despite a year's planning, today's high-powered arrivals were greeted by some disconcerting slip-ups. Several passengers on President Reagan's plane commented on what appeared to be security so subtle that it barely existed at the Cancun airport. Meanwhile, some Americans quietly worried about the background and motives of heavily armed security men from other national contingents.

Some of the airport security vacuum may have sprung from the confusion that came in with crowds of part-time presidential cheerers supplied by the Mexicans to show the dignitaries suitably organized enthusiasm.

Buses brought down from Mexico City to give Cancun an instant transportation system were filled last night with contented local peasants who had just dined at Mexican government expense as their reward for their ecstatic reception of Mexican President Jose Lopez Portillo yesterday. Subsequent dignitaries mostly got uniformed school children.

When Reagan arrived he found instead of the red-white-and-blue bunting meant to greet him, the colors of India that had graced Gandhi's entrance only 18 minutes before and could not be replaced in time.

What most upset the Mexicans' careful planning was when Reagan arrived at the hotel, where Mexican Foreign Minister Jorge Castenada was waiting in the lobby to greet him and send him off to his suite of rooms. The Secret Service made a sudden change in plans. Sweeping past Castenada's outstretched hand, the U.S. delegation headed for a back service stairway, where Reagan led the entourage in climbing up six flights of stairs.

Because what is known of Reagan's policy position is in such sharp contrast to the stance of most other participants, and because the United States is the United States, most attention here has revolved around the separate press center set up in the Calinda Hotel by the White House.

The Mexicans, however, aware that the Ottawa summit was almost totally dominated by the effusive press releases and briefings of the Americans, are working hard to provide some alternatives to Washington's viewpoint and plan to mount their own briefings in the official press center they set up for the occasion.

Other countries are less organized. The Japanese press and public relations officials mostly talk to themselves in the pre-Colombian modern Casa Maya hotel.