PARIS, AUG. 9 -- President Francois Mitterrand announced today that France will expand its naval force in the Persian Gulf and send ground units and advisers to Saudi Arabia but that it will not join the multinational defense command being assembled there under U.S. leadership.

Mitterrand told reporters that Saudi Arabia had made no formal request of France to join such a group, but he acknowledged that "some non-official conversations" with Saudi and U.S. officials had raised that possibility. Any eventual military action, he stressed, would be carried out "in cooperation and coordination" with the United States "but only under French officers."

In London, meanwhile, British Defense Secretary Tom King said Britain will add a flotilla of coastal-patrol vessels and three minesweepers to its already strong naval force in the region and is sending two squadrons of fighter planes and Jaguar ground-attack aircraft to join the American-led defense buildup. The Jaguars are considered particularly effective against tanks and were seen as useful in stopping an Iraqi armor drive into Saudi Arabia.

But there will be no ground forces in Britain's deployment, King said, although he declined to rule out sending troops at a later date. "We considered whether it would be sensible" to rush troops to an area that "is obviously not the easiest climate for infantry," King said, "but what we wanted to do was to make the most effective immediate contribution towards helping to protect the territory of Saudi Arabia."

Australia said late today that it, too, would take part in the combined naval effort in the gulf and would send the guided-missile frigates Adelaide and Darwin to the region within five days.

French Defense Minister Jean-Pierre Chevenement said the aircraft carrier Clemenceau, which carries fighter-bombers and helicopters, would be among the vessels France would add to its naval presence in the gulf. Already on station there are a French frigate armed with deadly Exocet missiles and two smaller warships.

The size of the French ground force being committed to the region was unclear, but Chevenement said detachments including antiaircraft-missile units and technical advisers are being sent to Saudi Arabia and the United Arab Emirates to help guard against possible attack by Iraqi troops now arrayed along Kuwait's southern border.

Mitterrand said the enlarged French naval force will seek to enforce the arms and oil embargoes against Iraq and occupied Kuwait that were imposed Monday by the United Nations and the 12-member European Community. But he said another important mission of the fleet would be to evacuate an estimated 420 French nationals who now appear trapped inside Iraq and Kuwait.

Mitterand described the French citizens as "prisoners" and said that "the preoccupying character of this state of affairs has driven the government to give the order to French warships to be completely ready" to repatriate them.

As Arab leaders gathered in Cairo for a conference described by Jordan's King Hussein as their "last chance" to stave off foreign military intervention in the gulf, Mitterrand said he wished to allow every opportunity for the conflict "to be resolved by the Arab community." But, he added bluntly, "if that proves impossible, France will assume its own responsibilities."

Asked if French arms sales to Iraq and the close political relationship between the two countries during the 1980s might have contributed to the current crisis, Mitterrand responded testily that French military support to Iraq was justified by the threat to the entire Arab world posed by Ayatollah Ruhollah Khomeini's Islamic revolution. He said that France's "long and friendly relations" with Iraq and the support it provided during Iraq's war with Iran gave greater authority to French condemnation of the Iraqi invasion of Kuwait.

The French arms industry has come under attack in recent days for its massive supplies of sophisticated weaponry to Iraq over the past decade, which helped Iraqi leader Saddam Hussein to modernize his armed forces and acquire the most feared arsenal in the Arab world. French firms have delivered more than 100 Mirage fighter planes, 600 Exocet antiship missiles, 1,000 Roland surface-to-air missiles and 6,000 Hot and Milan antitank missiles to Iraq since Mitterrand was elected president in 1981.

While the Soviet Union has provided Iraq with the bulk of its conventional weaponry, the advanced aircraft and missiles sold by France have greatly enhanced Saddam's firepower. It was two Exocet missiles, apparently fired mistakenly by an Iraqi warplane, that struck the USS Stark and killed 37 seamen in 1987 while the vessel was escorting Kuwaiti-flagged tankers through the Persian Gulf during the Iran-Iraq war. France suspended all arms deliveries to Iraq last year because of a debt repayment dispute.

Britain's Tom King said he expected that other Western countries would soon join in the U.S.-led multinational gulf defense force and that he had been in touch with his European counterparts in NATO to try to win their commitment to the joint effort. British officials said they hope other countries will announce their participation during a meeting of Western alliance foreign ministers' in Brussels on Friday.

Italian Premier Giulio Andreotti told British Prime Minister Margaret Thatcher today that Italy would offer use of bases on its territory but that so far it had not been asked to join the multinational defense force, according to Italian news services. Portugal, West Germany and Spain also have offered use of bases.

Canada and the Netherlands, among several other European nations, have said they will decide whether to take part after the Brussels meeting. Washington Post correspondent Glenn Frankel in London contributed to this report.