The Pentagon and the State Department yesterday both rejected Soviet claims that the Reagan administration's new "Dense Pack" plan for basing the MX missile violates strategic arms limitation talks (SALT) agreements with the Soviet Union.

"Moscow is wrong," Assistant Secretary of Defense Richard N. Perle told a group of reporters.

Perle reiterated Pentagon assertions that the MX plan does not technically violate previous agreements.

But he also went further to say that Soviet efforts to stop the United States from responding to a Russian missile buildup achieved by "shamefully exploiting" loopholes in previous SALT agreements make a "mockery" of those agreements.

Under questioning, he also sought to put Moscow on the defensive by wondering again whether the Soviets have violated those agreements by secretly deploying an outlawed missile, the SS16. State Department spokesman John Hughes portrayed the basing plan for 100 MX missiles as "a limited deployment which will not impede carrying out substantial reductions in strategic arms" by both superpowers, as proposed by the administration in nuclear arms negotiations with the Soviets at Geneva.

Hughes said the MX "need not produce an increase" in the number of missiles or missile warheads because "it can be accommodated under the reduced ceilings" proposed by the United States in Geneva.

"It is in no way contradictory to the object and purpose of the SALT agreements," Hughes said, or "the specific provisions . . . concerning fixed launchers."

The officials talked with reporters one day after an editorial in the communist party newspaper Pravda charged that the decision to deploy the MX in the Dense Pack formation of 100 new underground silos "runs counter to one of the central provisions of the SALT I and SALT II accords -- an obligation not to create additional silos for intercontinental missiles."

A number of American critics of President Reagan's Dense Pack plan, including Carter administration SALT negotiator Paul Warnke and Sens. Carl Levin (D-Mich.) and Gary Hart (D-Colo.), also have said that the plan to build new underground silos violates the earlier SALT agreements.

Both the 1972 and 1979 SALT agreements state that "each party undertakes not to start construction of additional fixed ICBM [intercontinental-range ballistic missile] launchers."

Although the United States never ratified the second agreement signed by Carter and the late Soviet president Leonid I. Brezhnev in 1979, President Reagan pledged earlier this year that the United States will not undercut these accords as long as Moscow does not.

Perle repeated yesterday the Pentagon's basic claim that the MX is designed to be transported from one vertical silo to another and carries its launch equipment with it in a cannister.

Thus, the missile's underground silo is for protection against attack and is not a launcher, he said.

This explanation has been criticized because there are only 100 such silos and 100 such missiles.

This is in sharp contrast to the Carter administration plan, which envisioned shuttling 200 MX missiles and their launch equipment among 4,600 less secure shelters in a huge shell game meant to confuse Moscow.

Perle said yesterday that "the more fundamental reason" Moscow is wrong is that the intent of the initial SALT agreement was to freeze the huge Soviet missile buildup then in progress so that the American force of 1,000 Minuteman missiles would not be threatened by Soviet attack.

But Perle said there were many loopholes in that 1972 treaty which allowed the Soviets, without adding new silos, to modernize existing ones and to replace single-warhead missiles with newer ones carrying six warheads or more.

Some of the 1972 provisions against new launchers, he said, were carried through "mindlessly" in 1979. Thus, he argued, to take the earlier American effort to restrain Soviet missile power in SALT and "turn it around a decade later to prevent us from responding to the growth of their ICBMs . . . would make an absurdity of the whole SALT process."

When a Pentagon reporter asked about the disputed Soviet SS16 missile, Perle said there "was some considerable evidence that could well have indicated a violation" or "action inconsistent" with prohibitions in SALT II against deployment of this relatively small, mobile missile.

Perle said the matter "is presently the subject of discussion" and made clear he was not absolutely certain that the missile is deployed.

The status of this missile has been the subject of disputes behind the scenes for many years, and thus far the United States has refrained from charging that it is deployed in violation of SALT.

Intelligence officials have said that there was no hard evidence indicating the missile was deployed in any operational sense and that it did not appear to be a very good missile anyway.

Raising this issue publicly while the administration is under pressure from the Soviets and critics at home about whether the Dense Pack deployment of MX is a SALT violation will add to an already complicated debate.

In another development, senior defense officials said yesterday that, despite continuing reports from West Germany, there were no American plans to put more than the planned 108 new Pershing II missiles in that country.

Officials said that at one time there was some consideration of such a move and some people thought it was a good idea, but that it was never acted on.

The Pershing missile launcher can be reloaded once the first missile is fired.

But officials stressed yesterday that only 108 missiles plus some spares, but no complete extra missiles with atomic warheads, would be shipped to West Germany.

Officials also said that when Defense Secretary Caspar W. Weinberger meets in Belgium next week with other North Atlantic Treaty Organization defense ministers, he will "stress the continuity of this administration with every postwar administration" on U.S. nuclear war policy. It will be explained that American policy has been evolutionary "and there has been no abrupt departure." Because of the Reagan administration's own rhetoric and some portrayals in the media, there has been deep concern in Europe that the United States is now more inclined to think a nuclear war can be prolonged and won.

Weinberger, officials said, will also present an important new paper on ways that new technology can be used to greatly improve the effectiveness of western defense in central Europe using conventional rather than nuclear weapons.

The officials cited new cruise missiles that will eventually be accurate enough to score direct hits using conventional rather than atomic explosives on Soviet support targets deep behind the front lines.