Karachi. Pakistan. President Yahya Khan, in a hard-hitting broadcast to the nation yesterday, in which he warned of tough action by the Army if the politicians failed to prevent the country from splitting permanently in two, announced that the postponed session of the new Constituent Assembly would now take place on March 25. The original date - last Wednesday - was canceled because West Pakistan leader Zulfikar Bhutto threatened to boycott the Assembly. He had been angered by East Pakistan leader Sheikh Mujibur Rahman’s demands for greater autonomy for his province. Mr. Bhutto said today that he will attend the March 25 session.

The President’s broadcast was made against a background of mounting speculation that Sheikh Mujibur will make a declaration of independence for his state when he addresses a mass rally in Karachi today. His followers said that he would make an “historic statement.” The President himself sees the March 25 session as the final chance for Pakistan to frame a constitution which could lead to an easing of tension between the nation’s two wings and put an end to the rioting which is reported to have claimed 173 lives in East Pakistan last week.

For the first time since he assumed power in 1969, the President lashed out at the political leaders of East and West Pakistan - and particularly at Sheikh Mujibur. “Let me make it absolutely clear”, he said, “that, no matter what happens, as long as I am in command of the Pakistan Armed Forces and head of State, I will ensure the complete and absolute integrity of Pakistan. I have a duty towards millions of people in East and West Pakistan to preserve this country. I shall not allow a handful of people to destroy the homeland of millions of innocent Pakistanis.”

He said that Sheikh Mujibur had not responded to his invitation to attend a meeting of all political parties in Dacca next Tuesday. He hoped that his decision to hold the inaugural Assembly session on March 25 would elicit a “patriotic response” from every political leader in Pakistan.