A weary Andres Rosenthal interrupted his rum and coke at an outdoor cafe to give orders over a walkie-talkie. There seems to be no end to last-minute details as this resort readies itself for a supersummit of 22 nations.

A few hundred yards out on the clear Caribbean waters Mexican gunboats cruised the periphery of the island. Helmeted soldiers in camouflage uniforms strolled among the deck chairs on the beach.

Technicians busily tinkered with huge satellite antennas, 1,000 telexes and 300 telephones, while 2,400 journalists made their way to hotels already packed with 1,500 diplomats, bureaucrats and security men.

Three Medevac helicopters tested their engines. Neurosurgeons and cardiac specialists are on call.

Cooks from presidential palaces around the world sorted their sushi and checked their chickpeas.

Rosenthal, a ranking member of the Mexican Foreign Ministry, has worked for more than a year as the summit coordinator, getting these $8 million worth of preparations in order.

As he put down the walkie-talkie he said, with what may have been a bit of wishful thinking, that in the light of meetings at Ottawa and Melbourne earlier this year, "summitry has become somewhat routine."

In fact there is nothing routine about the two-day meeting of 22 national delegations, including 17 heads of state, that begins here Thursday.

Whether the encounter in Cancun will begin to resolve the deep divisions between rich nations and poor nations that it is designed to address remains open to question, but it is unique in bringing together so many heads of state from nations of such disparate political and economic systems.

"Security is tight," said Rosenthal. "The reasons are obvious. Cairo, Washington, Rome."

Although bodyguards from each country accompany the various leaders, the basic business of protection has been left up to Mexico.

This 14-mile-long instant resort of Cancun, which did not exist a decade ago, was chosen as the site for the conference partly because of its relative isolation on the tip of the Yucatan Peninsula. The year-old Sheraton Hotel, where the leaders will stay, is some distance from the beach strip occupied by most of the resort's hotels, and a special highway has just been completed from the Sheraton directly to the airport.

There are no official figures on the number of Mexican security personnel and soldiers now working on the resort, but it is estimated that there are at least 5,000.

The challenge has been to maintain a relaxed atmosphere in the face of all the necessary precautions, but despite rumors that the resort would be sealed off for a month, "Cancun is still open for business," said Rosenthal.

Earlier attempts to begin a serious dialogue between the poor nations of the Southern Hemisphere and the industrialized nations of the North have foundered amid conflicting policies and been lost amid bureaucratic disputes. Here, it is hoped, the world may get away from official posturing and into a more direct and fruitful give-and-take among people who have full decision-making authority.

Mexican President Jose Lopez Portillo will take the Sheraton's presidential suite, and the quarters for the 21 other delegations are identical.

Some leaders, apparently dissatisfied with such homogenous surroundings, have made special arrangements. Philippine President Ferdinand Marcos, for example, flew his own furniture to the resort to decorate his quarters. Ronald Reagan's cook has been here for four days.

But from the Mexican point of view, Rosenthal said, "All 22 are being treated exactly alike, all the way down to their jacuzzi. It's the exact same size and warmed to the same temperature in every suite -- it's very democratic."