The Soviet Union sharply rejected as "routine fabrication" a Pentagon study of Soviet military power today, saying its publication was designed to "fool" NATO allies and obscure American efforts to gain strategic superiority.

The commentary in the Communist Party newspaper Pravda also raised doubts about Defense Secretary Caspar W. Weinberger's grasp of military affairs and quoted his predecessor and other "authoritative" U.S. military officials to rebut his argument about a shift in the East-West military balance.

Privately, officials here expressed surprise about the release of the Pentagon document one day after Secretary of State Alexander M. Haig Jr. met Soviet Foreign Minister Andrei Gromyko in New York.

As one source put it without elaboration, "This shows that the Reagan administration does not speak with one voice" on key issues.

There were no indication here that the meeting had produced any breakthroughs. The sketchy information suggested that both sides presented their basic concerns along lines articulated by presidents Reagan and Leonid Brezhnev.

Set against the Haig-Gromyko meeting and the announcement Tuesday by Eugene Rostow, head of the U.S. Arms Control and Development Agency, that SALT would resume early next year, the publication of the Pentagon document is likely to raise questions as to whether Haig was speaking for the administration, according to diplomats.

A Soviet source said that American pronouncements could be seen as an indication that the Reagan administration had yet to find its center of gravity.

Late tonight, Tass news agency quoted a CBS television news report, similar to one in The Washington Post today, that Reagan already had decided to deploy the system of mobile strategic MX missiles. Tass said the move was bound to whip up the arms race.

"In the light of the decision it becomes clear why the Pentagon and the CIA simultaneously released another anti-Soviet fraud." Tass added that the Pentagon booklet was needed to counter "the growth of the public movement in the United States for reduction of excessive military expenditures."

The Pravda commentary seemed designed to undermine American credibility in Western Europe. It called Weinberger's "colorful pamphlet" a phony document prepared with the help of "CIA disinformation experts" and said its goal was to intimidate and misinform the public in Western Europe.

It described Weinberger as "the conductor of a new anti-Soviet campaign" using "false" information to substantiate allegations that the Soviet-American military balance has been upset in the last 15 years and that it is now in Moscow's favor.

Pravda cited statements "by persons authoritative in military matters" that there is approximate parity in both the strategic and conventional East-West military balances. Among those cited are former defense secretary Harold Brown, Gen. David C. Jones, chairman of the Joint Chiefs of Staff and Haig when he was the NATO commander.

"For some inexplicable reasons, Weinberger did not share with the reader the secret of how he, a person who is rather distant from military affairs, managed within a matter of several months to disprove the serious conclusions by his predecessor" and other authoritative U.S. military spokesmen "about the existence of parity in the military might" of the two superpowers, Pravda said.

Pravda said that the devices used by the Pentagon -- "the maps, figures and diagrams" -- recalled similar efforts to justify sharp increases in military expenditures during the Truman and Kennedy administrations.

"The smokescreen about an alleged Soviet threat," it continued, is being used to counter "the wave of antiwar protests in Western Europe" and to disguise American efforts to upset the current balance of forces.