PARIS -- The American diplomatic campaign to isolate Iran and compel an end to the Iran-Iraq war is beginning to falter, undermined by secret deals that Tehran has been able to strike in recent weeks with France and the Soviet Union.

As painful as it is to see good in anything that benefits Iran's ayatollahs, this could be a cloud with a silver lining. It may force the United States to look seriously at the massive military force it has assembled in the Persian Gulf, at an annual cost of $200 million, and determine what it should be doing there.

The American armada has been described in Washington as supporting the diplomatic campaign to pressure Iran to begin peace talks with Iraq or suffer sanctions voted by the Security Council. But these goals appear increasingly difficult to achieve.

"They do not want peace, they want Saddam Hussein's skin," a European official deeply involved in this conflict says of the Iranians, dismissing the idea that Tehran will ever come to a bargaining table with Iraq's ruler. "They want to break Iraq apart. And all the Security Council resolutions will not change that. They are pursuing a dedicated, skillful strategy that will soon outflank the Americans."

The French package deal surfaced last weekend with the sudden release of two French hostages in Beirut and the French decision to allow the departure from France of Wahid Gordji, an Iranian Embassy translator wanted for questioning in a terrorist case. Tehran and Paris are now speaking publicly about moving toward more normal diplomatic relations, broken off last July after Gordji took refuge in the Iranian Embassy here.

The arrangement Iran has struck with the Soviet Union is still largely secret, but its outlines are clear for some western and Arab diplomats here. Iran has reportedly cut its support for Afghan guerrilla forces and stopped stirring up religious sentiment among Moslems inside Soviet Central Asia, while the Soviet Union has reciprocated by helping stall a vote in the Security Council on sanctions against Iran.

The Soviets insist that Iran must be given enough time to provide a clear yes or no to the U.N. peace proposal that has been presented to both sides. Iraq has accepted the plan while Iran has said it neither accepts nor rejects the idea.

Iraq's foreign minister, Tariq Aziz, complained publicly about the Soviet support for Iran's delaying tactics in remarks he made Monday to British journalists in Baghdad. Such a complaint is unusual for the Iraqis, since the Soviet Union provides about 80 percent of Iraq's military hardware.

Iraq's only other major arms supplier is France, the other primary target of the new Iranian campaign of diplomatic opening.

The most curious aspect of the jointly choreographed Soviet-Iranian stall has been the American refusal to force a public showdown with the Soviets over the sanctions vote. The United States would then at least profit in the Arab world by having the Soviets' opportunistic deal with Iran exposed to the light of day.

The best speculation heard here seems to be that President Reagan hopes to pull a rabbit out of his summit hat in Washington next week and get the Soviets to agree to joint action on an arms embargo against Iran.

But there are no evident grounds for optimism that this will happen, unless Reagan is prepared to give some commitment to reduce significantly the American fleet now on duty in the gulf. This would be an important enough accomplishment for Mikhail Gorbachev to justify his passing up the advantages that Iran's conflict with the United States now offers the Soviets.

But it would also be a major jolt to the Arab states that the U.S. naval force was brought to the gulf to reassure. They would point to a quick reduction as another sign of America's diminishing power and resolve.

The fleet, in other words, stays in the gulf because it cannot afford to leave. This circular logic, particularly at the high cost this deployment involves, is a trap rather than an opportunity. It is time to begin, slowly and as invisibly as possible, to draw down the U.S. naval armada. This slow restructuring should leave a force that is larger than the pre-crisis average of three ships but still small enough to be viable for the long term.