WARSAW, Poland (AP) _ The Interior Ministry began a review Wednesday of documents that purportedly show its secret police spied on Prime Minister Tadeusz Mazowiecki's government as it took power from the Communists.

The documents were presented by the conservative, anti-Soviet political party Confederation for an Independent Poland, known by its Polish initials KPN. The papers are said to describe activity by the security services under Interior Minister Czeslaw Kiszczak, who remained in the new government as a Communist holdover.

Dated from August and September 1989 - Mazowiecki was elected on Aug. 24 and the East bloc's first non-communist government was seated on Sept. 12 - the reports analyze the activities of Lech Walesa, potential splits in Solidarity, and debates by former Communist-linked parties that joined the new coalition.

Krzysztof Krol, a KPN leader, on Tuesday made public some of the documents he said were passed to him by an unidentified informer. He said the originals were in his possession and would be handed over to the Justice Ministry.

Spokesman Wojciech Garstka of the Interior Ministry went to KPN offices Wednesday and took notes on the documents. He expressed skepticism about their authenticity but reserved further comment.

Krol said the papers ''prove that the security service under Gen. Kiszczak, at least with the knowledge of President Jaruzelski, spied on the government of Prime Minister Tadeusz Mazowiecki.''

Kiszczak was one of four Communists who remained in Mazowiecki's government. Wojciech Jaruzelski, the former Communist Party first secretary who imposed martial law in 1981, was given the presidency in July largely to smooth relations with the Soviet Union.

The transitional concessions to the Communists resulted from historic negotiations that ended the party's 45-year grip on power. At the time, Poland was the only country that had gone so far.

But as reform swept Eastern Europe, the continued presence of former Communists in the government became a source of controversy. Walesa, leader of the Solidarity union, and many Poles have agitated for their removal.

The documents are addressed to Jaruzelski, Kiszczak and a senior Interior Ministry deputy, according to the Gazeta Wyborcza daily.

Mazowiecki will go before parliament Friday to unveil a shakeup in his government, struggling to surmount an avalanche of criticism from farmers and Walesa.

This was disclosed Wednesday by Solidarity parliamentary leader Bronislaw Geremek at a meeting of his caucus.

Government spokesmen declined information on what changes were under consideration.

The shock economic reform program embarked on by Mazowiecki and his deputy prime minister, Leszek Balcerowicz, has prompted harsh protests from various hard-hit sectors.

Among those protesting the loudest are Poland's 2.5 million private farmers. Roman Bartoszcze, leader of the Polish Peasant Party which competes with other groups to represent rural interests, suggested Tuesday that his party's four ministers quit the government.

Walesa wants Mazowiecki to replace holdover Communists in the government, hold early parliamentary and presidential elections and speed privatization of state enterprises.

The government also is grappling with a major rail strike.

Walesa is widely believed to be gearing up to run for president to replace Jaruzelski.