The Reagan administration, in a tough new rhetorical attack on the Soviet Union, charged yesterday that massive Soviet military maneuvers near Poland may be an attempt to intimidate the Polish people, and accused Moscow of being "ultimately responsible" for an armed incursion by Afghanistan into Pakistan.

In addition, the administration said, the disclosure by the Soviet news agency, Tass, that 100,000 troops are participating in the maneuvers near Poland means that Moscow has violated the 1975 Helsinki accords by failing to officially notify the other signatory nations about the strength of the forces involved in the exercise.

The so-called "confidence-building" provisions of the accords--signed by 35 nations, including the Soviet Union and the United States--call for such notification when a participating country stages maneuvers involving forces of 25,000 or more. State Department officials said yesterday this is the first instance in which the Soviets have failed to provide such information.

The State Department first complained about an apparent Soviet violation of the nonbinding agreement in a public statement Friday. Yesterday, department spokesman Dean Fischer volunteered another statement charging that the Tass disclosure proved there had been a violation.

Fischer's statement, coupled with another that he made about the raid into Pakistan, appeared to be part of the administration's strategy of vocally challenging each incident it regards as a breach of "internationally accepted conduct" by the Soviets.

In addition, the administration seemed to be warning Moscow against trying to unduly pressure the dissident Polish Solidarity union movement, which is meeting to plot strategy in dealing with Poland's communist government.

Charles H. Thomas, a State Department official dealing with East-West security affairs in Europe, said "one can only speculate" that the maneuvers are "related to the fact that the Solidarity conference is going on at the same time."

Fischer, in his statement, said, "It raises serious questions about the Soviets' professed interest in measures designed to build confidence and enhance stability in Europe." He added that the incident underscores the need for any conference on European disarmament--an idea being pushed by Moscow--to contain safeguards proposed by the West.

In regard to the Afghan raid against Pakistan, Fischer noted that there have been five such incidents since the Soviets invaded Afghanistan in December, 1979, and he charged that since Moscow controls the Afghan government, the United States holds "the Soviet Union responsible for threats to Pakistan's security emanating from Afghanistan."