France declared today its decision to both strengthen its strategic nuclear forces and proceed with development of neutron weapons in order to preserve its nuclear independence.

"France's policy is not at all neutralist . . . . France intends to remain faithful to its allies, with the United States in the forefront," Prime Minister Pierre Mauroy told the Institute of High National Defense Studies in a speech marking his first such comprehensive review of Socialist military policies.

However, Mauroy rejected the U.S. strategy of graduated response in case of Soviet and Warsaw Pact aggression, a strategy that Europeans fear invites widespread destruction within Europe. Conceding control over the enhanced-radiation weapon to the United States, he said, would make Europe "just a rung on the ladder of violence and not the supreme end of [American] defense policy."

"It would not be rational to renounce beforehand acquisition of an arm that could increase our deterrent potential," he declared.

Thus the controversial weapon will be added to France's arsenal of 80 submarine-launched ballistic missiles and 18 intermediate-range ballistic missiles.

Paris under the Socialists seems to be following a two-track approach to foreign policy--agreement and cooperation with Washington on meeting Soviet power with equivalent Western might in Europe, but disagreement on origins of turmoil in the Third World and the best way to respond to such turmoil.

President Francois Mitterrand has, for example, emphasized the need to be firm with the Soviet Union on such matters as its intervention in Afghanistan and deployment of SS20 missiles in Eastern Europe. Such statements have won praise from the Reagan administration despite its early jitters at the idea of a Socialist government that included communists in the French cabinet

Mitterrand has drawn a clear distinction, however, between French and U.S. policy toward the Third World, going so far last week as to call Reagan's policy on Central America "simplistic."

An independent nuclear force has been a keystone of French defense policy since then-president Charles de Gaulle pulled out of the North Atlantic Treaty Organization's integrated command in 1966, remaining an Atlantic Alliance member but reserving the right to make his own decisions on when to push the nuclear button.

"The government is perfectly aware of the fundamental contribution for the balance of forces of American deterrence," Mauroy said, falling in line with the 15-year-old Gaullist doctrine. "But how can we miss seeing that this American deterrence is designed to protect the United States, for sure, the Western camp, of course--and not only France. I almost said, but not France first."

Former president Valery Giscard d'Estaing already had revealed that France was experimenting with neutron warheads. But the Mitterrand government's attitude to the controversial weapons had been ambiguous before today.

U.S. plans to produce neutron weapons have met with loud opposition in some Western European countries and particularly biting condemnation from the Soviet Union. In France, however, opposition has been limited and there is little sign of the movement calling for unilateral nuclear disarmament that has sprung up in neighboring Western countries.

There was no outcry, for example, when Defense Minister Charles Hernu announced June 2 that newly socialist France would resume testing nuclear bombs in the South Pacific--only four days after announcing the tests were suspended for a "complete study of the files."

French resolve to proceed as well with development of neutron weaponry could reduce the impact of opposition to the Reagan administration's own plans.

On one hand, it spreads the burden, giving opponents, especially the Soviet Union and European leftists, two targets instead of one. On the other, it is the decision of a Socialist government that contains four communist ministers whose party is traditionally attentive to Moscow.

Georges Marchais, the French Communist Party leader, refused in an interview over the weekend to make a public judgment of Mitterrand's first 100 days in power. He underlined instead a "very big discussion" in the party leading up to a congress scheduled at the beginning of next year.

Socialists and communists have been going out of their way in public statements to say how well they are getting along in the government. French analysts have been wondering out loud, however, how much of the "very big discussion" concerns the gap between communist positions--on such issues as neutron weapons--and French positions that French communist ministers are party to.