The French Defense Ministry refused yesterday to confirm or deny that France has exploded a neutron bomb at its South Pacific test site, intensifying speculation that there is something to press reports here.

Officials at the presidential palace and foreign officials who follow French military affairs denied privately that there was anything to a front-page story in the mass-circulation newspaper France-Soir headlined, "France has the Neutron Bomb." It followed a similar report earlier by the newsweekly Le Point.

France is studying the possibility of developing high-radiation antitank shells, popularly known as "neutron bombs," informed sources say, but there is no indication that there has been anything beyond feasibility studies.

French development of the weapon could be politically attractive for President Valery Giscard d'Estaing because it would give him an advantage in his continuing debate with the Gaullist Party, which is constantly suggesting that it defends French national security interests better than the government does.

It would also be useful to Giscard in his drive to intensify relations with West German Chancellor Helmut Schmidt who has expressed his distress over President Carter's decision to hold back on making the tactical nuclear weapons.

Informed betting in Paris is that France will never actually produce such antitank shells because of the cost and because of the fudemental shift it would imply in French nuclear strategy.

[In Washington, a key official of the Department of Energy, associated with the U.S. neutron weapons program, said it was possible that the French over the past years or so had tested a low-yield hydrogen or fusion device as "proof of the principle" that radiation in such cases exceeds blast and heat. While it might not have been thought of as a "neutron bomb" at the time, he said it could be now because the controversial American project has brought attention to the concept of the weapon.]

The news stories come at an embarassing moment of Giscard, as he is preparing to make a major presentation next month to the special U.N. General Assembly sessions on disarmament. Under Charles de Gaulle, Fance left its chair empty at all international disarmament conferences and Giscard proposes to modify the organization of conferences so that France could take part.

None of the experts doubt that France has the scientific capability to produce the same effect as a neutron shell experimentally - a hydrogen explosion with increased radiation and minimal heat. Miniaturizing such a device, so it could be carried by an eight-inch shell, is thought to present more problems, but they are not considered insuperable if the French are willing to spend the money.

The best guess is that it would take France about $1 billion a year to develop the weapon, about half of its already tight nuclear weapons development budget. That probably would delay French efforts to equip its strategic nuclear forces with multiple warheads in the 1980s.

It would also mean new French stress on tactical nuclear weapons that would belie the time-honored French strategy of massive retailation. Unlike the U.S. and soviet nuclear arsenals, the French have limited capacity for a graduated battle field response. French nuclear forces have operated independently of the alliance since de Gaulle took France out of the military side of NATO in 1966.

The French have always said that they would only use their current tactical nuclear weapons as symbolic warning shots to demonstrate the earnestness of their intention to use their strategic nuclear strike force of plants, submarines and ballistic missiles.

In relation to American statements over the years that its nuclear stockpile has hovered around 7,000 war heads, the present French tactical force is thought to consist of fewer than 50 launchers with fewer than 150 rockets.