Pakistan's martial law government today placed most leaders of the country's political parties under house arrest after banning political activities and postponing indefinitely elections scheduled for next month.

Moving early this morning after President Mohammed Zia ul-Haq's radio and television announcement last night, police fanned through the country to the homes of political leaders and the offices of the parties.

According to reports in this morning's newspapers here, printed for the first time under strict government censorships, among those arrested were Nusrat Bhutto, widow of executed former prime minister Zulfiqar Ali Bhutto, and her daughter Benazir.

Mrs. Bhutto took over on her husband's death ass leader of the Pakistan People's Party, and Benazir has been the party's most vocal spokesman. They were placed under arrest in their Karachi house for three months.

Although banned by the government from taking part in the elections, which had been scheduled for Nov. 17, Bhutto's party had emerged as the focus of opposition to the 26-month-old martial law government.

Members of the Pakistan People's Party, running under the slogan of "friends of the people," scored well in last month's nonpartisan local election.

This strong showing, along with the maneuvering of politicians on election rules in an effort to place some distance between them and the martial law government, is widely believed by observers here to have spurred Zia to call off the election and strengthen martial law restrictions.

[In Washington, a State Department spokesman said the United States is "deeply disappointed" by the postponement of elections and that the U.S. view was relayed to Agha Shahi, Zia's foreign affairs adviser, who was in town for talks with U.S. officials.]

Zia's speech appeared to have been received calmly by people here. One observer said people were so tired of wrangling among politicians that they did not mind the elections being called off.

Moreover, the political leaders who could have organized demonstrations were silenced quickly and newspapers were placed under censorship.

Besides the Bhuttos, others placed under house arrest included the former chief of the Pakistani Air Force, Air Marshal Asghar Khan, who at one time was considered a Zia favorite to head a civilian government. Reports circulated that at least 20 lesser known politicians in Rawalpindi were arrested today.

"My guess is if they moved against the ones that were listed in the paper, they got more," said one diplomatic observer here.

Newspapers today were a pale shadow of themselves. Full of political speculation in recent weeks, today's front pages were dominated by the verbatim texts of the martial law regulations disbanding political parties and banning political activities, strengthening the martial law courts and establishing press censorship.

In addition to censoring all papers, the government closed two Urdu-language organs of the Pakistan People's Party -- the dailies Musawaat in Lahore and Karachi and Sadagat in Karchi.