Responding to moves seen here as deliberate rebuffs from the Reagan administration, France's Socialist government has decided to go ahead with a $15.8 million arms deal with Nicaragua signed in December, according to French officials.

The decision by French President Francois Mitterrand to end the delay in delivering two Alouette III helicopters to the Sandinista government in Managua is certain to continue the precipitous decline in French-American relations that broke into the open at the Versailles economic summit last month.

Mitterrand has been a strong supporter of President Reagan's strategic armament program and backed many of Washington's tough stands on the Soviet Union. When he visited Washington in March to hold preparatory discussions with Reagan on Versailles, he made it known that the helicopter deal, which was sharply criticized by the State Department, would face indefinite delays.

The head of Nicaragua's revolutionary junta, Daniel Ortega, is to arrive here from Managua Monday for a two-day visit that includes a meeting with the French president. The French decline to comment on the purpose of this visit, but they acknowledge that it coincides with increasingly tense Franco-American relations.

High U.S. interest rates and the dollar's surge against a falling French franc have been problems from the beginning for a French government committed to creating new jobs and beating back unemployment. The situation has been exacerbated by the Commerce Department's preliminary findings that some Western European countries have been subsidizing steel shipments, by U.S. restrictions on the use of American technology in West European equipment sales to the Soviet gas pipeline project and by the American veto of France's U.N. resolution on Lebanon.

Any new arms deal with the Nicaraguan government seems highly unlikely, but a Foreign Ministry spokesman contended that such a request would be considered "whether the Americans like it or not."

The Versailles summit disclosed a fundamental difference in view by Reagan and the Western European leaders on the usefulness of economic pressure on the Soviet Union. Mitterrand and West German Chancellor Helmut Schmidt in particular publicly said that the Reagan administration's apparent belief that restrictions on the construction of the pipeline would contribute to the collapse of the Soviet system was unsound. They also contrasted Reagan's eagerness to ask European consumers to make economic sacrifices to pressure the Soviets while the United States has lifted its own grain embargo imposed after the Soviet invasion of Afghanistan.