PARIS, SEPT. 15 -- President Francois Mitterrand announced today that France will send 4,000 ground troops backed by tanks and combat aircraft to Saudi Arabia and will seek to extend the sea and land blockade authorized by the United Nations against Iraq to cover air traffic.

The French head of state also said his government would expel more than two dozen Iraqi military attaches and intelligence agents affiliated with their embassy in Paris along with 26 other Iraqi military trainees on study programs here. Mitterrand said all other Iraqi diplomats would not be allowed to travel outside Paris.

The measures were taken at an emergency cabinet meeting today after Iraqi soldiers violated international law by forcing their way into the French ambassador's residence in Kuwait and taking away three French citizens. Mitterrand said he believes they had been moved to strategic sites to join hundreds of other Western hostages serving as human shields to forestall an offensive strike by U.S.-led forces in the gulf.

{In Baghdad, Iraqi President Saddam Hussein announced today that elderly or ill French nationals may leave Iraq starting Monday, news agencies reported. So far, only women and children have been allowed to leave.}

Speaking at a press conference after chairing the session with senior ministers, Mitterrand said he had detected "no sign coming from Iraq about avoiding armed conflict." He contended that the Iraqi leadership is displaying "a bellicose spirit that seems to measure risks badly, so we have to prepare ourselves."

The necessary agreements for the additional French air and ground forces being dispatched to the gulf would be worked out today during a meeting between French Defense Minister Jean-Pierre Chevenement and Saudi ruler King Fahd, Mitterrand said.

The 4,000 new French troops to be sent to Saudi Arabia will consist of three regiments. The first will be composed of infantry units equipped with anti-tank weapons, another will operate 48 attack helicopters, and a third regiment will be sent with 48 tanks and other armored vehicles. In addition, 30 more combat aircraft and their crews will be sent along with Mistral anti-aircraft missile units.

France already maintains the largest foreign military contingent in the gulf after the United States, with more than 4,000 men aboard nine warships and the aircraft carrier Clemenceau and 5,000 based in Djibouti.

The French ground forces are expected to coordinate closely with the multinational force of American and Arab troops in Saudi Arabia, but Mitterrand has insisted that France retain its independent military command.

Mitterrand stressed that French strategy is still based on strict enforcement of the global trade embargo on Iraq. He said it was particularly deplorable that there was already a "fairly long list" of countries and Western firms, including French enterprises, that have tried to circumvent the boycott and deliver goods to Iraq.

As a result, Mitterrand said that France, as one of the five permanent members of the U.N. Security Council, would propose a new resolution to expand the blockade to air traffic as well as land and sea transport. He said the council should also find ways to punish all countries and business firms that are rupturing the embargo. Mitterrand said he would personally ensure that any French companies caught trying to break the embargo "will pay dearly for their lack of national unity."

Referring to the past decade of friendly relations when Paris provided Baghdad with a formidable arsenal of sophisticated weapons, Mitterrand said it was particularly tragic that "the country that saved Iraq from defeat in its war with Iran should be the victim of this attack."

Nonetheless, he said he did not regret France's role in building up Iraq's military strength because otherwise Iran's Islamic fundamentalist revolution could have swept through the gulf and the rest of the Arab world. "At that time, the historical situation required us" to arm Iraq, Mitterrand said.