The Soviet Union tonight described as "clear and unambiguous" its rejection of President Reagan's proposals for an interim agreement on missiles in Europe and said official U.S. speculation that Moscow would change its position is "built on sand."

A statement by the official news agency Tass said that State Department officials "in their propagandistic fever" appear to have failed to "read carefully" the text of a press conference Saturday by Foreign Minister Andrei Gromyko. He had described Reagan's proposals as "unacceptable" and "not serious."

Responding to a State Department spokesman's statement Saturday that Gromyko's declaration was not Moscow's last word on the issue and that the Soviets may in fact be ready to negotiate an accord on the basis of Reagan's offer, Tass said that "the following words of Gromyko" should be noted in Washington:

"If the position of the United States remains as it was announced by the president, there are no chances for an agreement" at the Geneva talks on limiting medium-range nuclear weapons in Europe.

"That is why it would be good if the U.S. administration adopted a more objective position meeting the need to preserve the principle of equality and equal security, and fully taking into account the legitimate interest of the Soviet Union and of all the states of the Warsaw treaty."

Tass added, "Calculations by certain circles in the United States on a change in the clear and unambiguous stand of the Soviet Union with regard to Reagan's so-called interim proposals are built on sand."

Reagan's proposal called for the United States and the Soviet Union to agree to global parity in the number of medium-range nuclear warheads carried by land-based, medium-range rockets.

Gromyko said the proposal was "unacceptable" because it excludes forward-based U.S. nuclear strike aircraft and strategic aircraft on U.S. aircraft carriers in waters "around Europe" and because it fails to take into account the British and French nuclear deterrents. Gromyko also vigorously rejected Reagan's demand that Soviet medium-range nuclear weapons located in the Asian part of the Soviet Union be included in the Geneva talks.

Another Tass commentary written by military analyst Vladimir Bogachyov accused the State Department of "distorting" facts, "juggling" figures and "unscrupulously manipulating" data on the military balance in a "sordid attempt" to twist the meaning of Gromyko's message.

A commentary in the government newspaper Izvestia said the president's new proposal, like his zero option position, was designed to break the existing strategic parity.

"The term 'interim offer' renders accurately its substance if its authors were striving to build a bridge between the zero option and the scheduled start of the actual deployment" in December of 572 Pershing II and cruise missiles in western Europe, Izvestia said.

The offer is logical, Izvestia said, "if one considers Reagan's cynical explanation that the United States has never backed away from its intention to deploy the missiles on time."

At the same time, Tass tonight launched a blistering attack on Japanese Prime Minister Yasuhiro Nakasone, rejecting his claims that there were no U.S. nuclear weapons on Japanese soil and asserting that he "would be well advised to think where such a risky policy can lead his country rather than try to refuse what has become obvious."

The Tass statement came hours after Japan's ambassador here, Masuo Takashima, called on Premier Nikolai Tikhonov and told him that there were no nuclear weapons on U.S. bases in Okinawa or in any other part of Japan.

According to Japanese sources, Tikhonov did not go into details beyond complaining about Nakasone's "provocative statements" earlier about his government's intentions to make Japan an "unsinkable aircraft carrier" for the United States. But Tass went into great detail to refute the Japanese assertion. It cited Japanese press reports about the presence of nuclear weapons on Okinawa and quoted Edwin Reischauer, the former U.S. ambassador to Japan, as saying that that there existed "a secret verbal understanding" between Washingon and Tokyo permitting U.S. ships and aircraft carrying nuclear weapons to use Japanese ports and airfields.

Tass said the recent call at the port of Sasebo of an American naval squadron including, the aircraft carrier Enterprise, provided "evidence" that such understanding was still in effect. It also quoted retired U.S. admiral Gene La Rocque, as saying there were "at least 200" nuclear weapons aboard the ships in the squadron.

The agency also attacked Japan for permitting the United States to deploy F16 fighter bombers "in the north of Honshu." It said these aircraft were capable of carrying nuclear weapons and were designed for offensive operations.