The Island of San Giorgio, where the summit conference of Western leaders begins today, is a major achievement in the international campaign to save Venice -- an effort into which endless public and private funds from governments, foundations and the United Nations have been pouring for the past 30 years.

A Benedictine monastery was founded on San Giorgio in 982 and the present church which dominates the island was built in 1566. Various cloisters and dormitories were added across the next few centuries.

But then the island fell on hard times. It was taken over by the Uastrians in the days of the Austro-Hungarian empire and converted into military barracks and headquarters. It simply faded into neglect, disuse and decay between the two world wars.

Then, in 1951, the Italians organized to do something about it. A foundation was established with the dual purpose of rehabilitating the island's historic buildings and using them for a variety of social, educational and cultural activities.

The centerpiece of this effort is a school for study of Venetian civilization with a library of 150,000 ancient volumes, an archive of some 600,000 photographs, and about 2 million microfilm frames -- a worthy setting for a modern heads of government summit meeting.

ACCORDING TO history books, the last important summit to take place in Venice was more than 800 years ago, in 1177, when the Doge Sebastiano Ziani settled a power struggle between Emperor Frederick Barbarossa of the Holy Roman Empire and Pope Alexander III.

Barbarossa had descended on northern Italy with his armies, and the pope had fled to Venice which was then a republic. When Barbarossa then entered Venice, the great question of peace lay in whether he would abjure further conquests and pay homeage to the pope.

The Venetians, adroitly playing the middlemen, arranged a ceremony in the Basilica of St. Mark's where the emperor agreed to apologized for his aggressions by prostrating himself before a statue of St. Peter -- but not the pope. Alexander III, however, simply declared this obeisance to be before both St. Peter and the pope.

At any rate, Barbarossa went back to Mainz, which was then the seat of the Holy Roman Empire, the pope returned to Rome, and the Venetians went on being the middlemen of the Adriatic world.

FRENCH PRESIDENT Valery Giscard d'Estaing, whose motto is independence in all things, has managed to find a way even in this summit setting to stand apart from his fellow heads of government.

Instead of staying at one of the many available luxury hotels along the Grand Canal or close in to the conference island, the French president is housed at a hotel on the Island of Torcello, far away from everybody else. Thus, he will be the only chief of state to arrive and depart at the island of San Giorgio by helicopter, instead of launch.

President Carter and the American delegation are all installed in the grand comfort of the Cipriani Hotel, which has everything but a view of the Venice waterfront, since it is on a lagoon island with the city behind it instead of in front. The Americans brought along an entire White House telephone system.

Originally, the White House communications people proposed to simply take over the hotel switchboard and hook it up with the White House in Washington.

But the hotel manager demurred. He pointed out that this would mean that breakfast orders for orange juice, toast, coffee and scrambled eggs would have to go to Washington and back -- and this might effect the high quality of the Cipriani's room service.

Approximately 1,700 journalists are accredited for this jamboree. The White House press concentrated at the Excelsior Hotel on the Lido -- a lagoon island that shelters Venice from the open waters of the Adriatic, and takes about 15 minutes by boat from St. Mark's Square.

The Japanese, too, have put their correspondents and their press center in the Excelsior. The West Germans are in the Danieli Hotel a few hundred yards from St. Mark's and the British are at the Gritti Palace on the Grand Canal.

Countless boats are under charter either by the Italian government or by the television networks to shuttle delegates and reporters back and forth to the island of San 2giorgio which lies in the lagoon between Venice and the Lido.

For reporters, the biggest problem at the end of the day (or night) will be coordinating with each other on what the various national press briefings are producing up and down the Grand Canal. As Shakespeare wrote in the "Merchant of Venice." What news from the Rialto."