The Reagan administration, in a clear expression of disapproval of French President Francois Mitterrand's appointment of four Communists to his cabinet, warned yesterday that "the tone and content of our relationship as allies will be affected by the inclusion of Communists in that government or in any government of our West European allies."

The administration's concern was expressed in a lengthy statement issued by the State Department late yesterday after a day of intensive consultations with the White House. It paralleled in expanded form remarks made by Vice President Bush on his arrival in Paris yesterday for talks with Mitterrand.

The statement reflected the obvious discomfiture the French appointments have caused the administration, which has made anti-communism the centerpiece of its foreign policy but also has been seeking to promote good relations captured the French presidency and control of parliament. Bush's Paris visit, which was arranged before the appointment of the Communist ministers was announced, was a Reagan-inspired effort to cement a good working relationship with the new French government.

In the statement, the administration carefully referred to France as "a valued ally and friend," welcomed "the opportunity to continue excellent relations" and acknowledge France's right "as a sovereign democratic nation" to choose its own leaders.

But it added: "While we fully recognize and respect the right of the government of France to determine its own composition, it is a fact that the tone and content of our relationship as allies will be affected by the inclusion of Communists in that government or in any government of our West European allies."

The statement concluded, "Since the end of World War II, all United States administrations have pursued policies reflecting this view. Our policies have not changed."

U.S. officials refused to elaborate publicly on the statement. In private, however, administration officials said it was intended as a signal to Mitterrand and his Socialist Party that Washington sees several inherent dangers in their opening to the Communists and expects Mitterrand to guard against these, so as not to undermine the Atlantic Alliance.

"There's nothing we can do about it, and we're not going to commit suicide over their decision," one of U.S. official said. "But we're obviously concerned about the potential effects and precedents, and we want to make sure that Mitterrand understand that."

Specifically, the official added, the appointments seems certain, at least for the moment, to add an element of suspicion and caution to dealings between the two governments. In addition, he continued, the administration is concerned that the Mitterrand decision will have adverse effects on U.S. public opinion and cause doubts about the reliability of ties with North Atlantic Treaty Organization partners at a time when Reagan and Secretary of State Alexander M. Haig Jr. have put a high priority on reinvigorating the NATO alliance.

Finally, the official pointed out, there is concern here about the French precedent having a ripple effect in Western Europe. In Italy, another important NATO country whose domestic politics are strongly polarized between left and right, there have been increasing pressures on the non-communist left to attempt to take power with the support of the large Italian Communist Party.

Although France withdrew from military participation in NATO several years ago, it remains a highly influential member of the alliance in political terms, and its actions are certain to have profound psychological impact on the other members. Mitterrand, who told Bush yesterday that "France is a faithful and loyal ally of the United States," has insisted that the structure of his government is a purely internal affair and will not affect his country's adherence to western ideals in the foreign policy arena.