SAINT FRANCOIS, Guadeloupe--The crisis in Iran was the main topic of discussion as President Carter, British Prime Minister James Callaghan, French President Valery Giscard d'Estaing and German Chancellor Helmut Schmidt gathered yesterday on the Caribbean island for a two-day summit conference.

Zbigniew Brzezinski, Carter's national security advisor, said yesterday Carter would reiterate his support for Shah Mohammed Reza Pahlavi, who has the support of the other three leaders as well.

The leaders also discussed how the United States should negotiate the issue of "gray area" tactical nuclear weapons-- which pose a danger to major European cities -- in the Strategic Arms Limitation Talks with the Soviet Union.

Other issues covered included the new relations between the U.S. and China, the stalled Egyptian-Israeli peace talks, and world money and trade problems.