The Soviet government rejected again tonight U.S. charges that it had violated arms control treaties, calling a report by a bipartisan commission that President Reagan submitted to Congress last week "an open political forgery."

In a formal statement distributed by the government news agency Tass, Moscow charged that the United States had either flouted these treaties or was trying to undermine them.

Coming on the eve of Sunday's foreign policy debate between Reagan and Democratic challenger Walter F. Mondale, the Soviet statement appeared designed to focus attention on nuclear weapons and the Reagan administration's record in arms control.

"Soviet charges that the U.S. is violating arms control agreements are baseless," said State Department press officer Brian Carlson. "We have responded previously to these charges through diplomatic channels." He noted that the General Advisory Commission to which the Tass statement referred is an independent body whose report was sent to Congress at its request and without governmental approval.

The Tass statement dismissed as "trite and long-refuted inventions" U.S. allegations about Soviet violations or possible violations of the two strategic arms limitation treaties concluded in 1972 and 1979. It did so in general terms, without a detailed analysis.

Instead, the Soviets provided a list of their own accusations that focused on the most contentious aspects of arms control.

The two superpowers exchanged similar charges of treaty violations last January, each presenting a list of alleged violations similar to those in this latest exchange. The Soviet statement in that round was issued on the day that Reagan announced his candidacy for a second term.

The Soviets have alleged again that:

Washington's refusal to ratify the SALT II treaty, which was signed by presidents Jimmy Carter and Leonid Brezhnev five years ago, "vividly demonstrated how they in Washington approach the assumed obligations."

"New violations are being programmed" by the United States, including exceeding SALT II limits on the number of ballistic missiles with multiple warheads and "the construction of additional silo launchers."

The United States contends that the MX missile, under development, is clearly permitted by treaty. A Midgetman missile, if developed, would be in violation.

The United States was working to "undermine" the 1972 antiballistic missile (ABM) treaty. It charged that despite treaty restrictions, the United States is developing a mobile ABM radar station, that other radar stations have been deployed to serve as a possible basis for a country-wide ABM radar system and that an intercontinental ballistic missile of the Minuteman type was tested for antiballistic missile purposes.

The United States tested an ABM in June, noting that tests, unlike deployment, are permitted by treaty. The Soviet charge of a mobile radar echoes charges made in the United States of such a Soviet violation.

Reagan's "star wars" program to develop a space-based defense against ballistic missiles, it said, was an "encroachment" on the ABM treaty.

The U.S. response to this charge has been that Reagan's program is for research, which the treaty specifically permits.

"At a time when the Soviet Union strictly and unswervingly observes the treaties and agreements it has signed, practical actions have been and are being taken on the part of the United States aimed at circumventing and directly violating its international obligations," the statement said.

It described Reagan's report to Congress as an exercise in "unseemly methods -- namely to ascribe to the other side its own misdeeds in order to try to camouflage this kind of behavior."