RAWALPINDI, Pakistan, Dec. 19—An official spokesman said here tonight that Pakistan's President, Agha Mohammad Yahya Khan, had decided to re sign as soon as he “hands over power to representatives of the people tomorrow.”

Zulfikar Ali Bhutto, the Deputy Prime Minister, is scheduled to arrive here from Rome tomorrow after having led Pakistan's case before the United Nations in New York. He is expected to become chief of government and may also be chief of state.

The sudden announcement about General Yahya Khan was viewed as the result of powerful military and civilian pressure on the President to resign following Pakistan's brief but disastrous war with India. Such pressure, especially from the Air Force, has stopped just short of a coup d'état and it was apparently made clear to the President that a coup would probably result if he did not step aside.

Date Was Set in June

However, tomorrow is also the date set last June for announcing a new national constitution. It had been expected that General Yahya Khan would retain the presidency for himself while convening a civilian government to administer the nation.

Official sources said tonight that a new constitution would be issued tomorrow, but there was no indication what form it might take.

Mr. Bhutto heads the leftist Pakistan People's party, which a year ago won the majority of seats allotted to West Pakistan in Pakistan's National Assembly. The convening of the Assembly and creation of the civilian government have been postponed by a series of political upheavals, a civil war and finally the war with India that ended Friday.

On Dec. 3, President Yahya Khan named Mr. Bhutto as Deputy Prime Minister and Foreign Minister. The President had named Nurul Amin, an aging Bengali, as Prime Minister to provide token representation for East Pakistan, the nation's most populous wing.

But last week Indian and local Bengali forces over whelmed Pakistani troops in East Pakistan and on Friday President Yahya Kim announced he had accepted an Indian cease‐fire offer.

Shortly after President Yahya Khan's announcement of ceasefire, Mr. Nurul Amin demanded that he resign. Subsequently, Mr. Nurul Amin announced that he himself was withdrawing and would not be Prime Minister.

There have been demonstrations in many cities during the past few days demanding continuation of the war and the ouster of President Yahya Khan. His house in Peshawar reportedly was burned down yesterday.

The harshest criticism today came from the retired chief of the Pakistani Air Force, who apparently spoke with the approval of friends serving as senior Pakistani officers.

The former Air Force head, Air Marshal Mohammed Asghar Khan, not only demanded President Yahya's immediate resignation, but also called for the public trial of the President on a number of charges.

Mr. Asghar Khan spoke at a press conference and a subsequent rally attended by several thousand people here.

“In the armed forces we proposed staff solutions for problems,” be said. “In the present case, Yahya has produced the perfect staff solutions for the destruction of Pakistan.”

The former officer, who heads a small middle‐of‐the‐road political movement, was an unsuccessful candidate for a seat in the National Assembly last year,

During the past year he has been an outspoken critic of the Yahya regime. He is said to have avoided arrest only be cause of his former high rank and continued influence in the Air Force, which he commanded during the 1965 war with India.

Today's rally at Rawalpindi's main Assembly grounds was closely guarded by riot police men but hostile gangs moved in, broke up the rally with firecrackers and sticks, and badly manhandled Mr. Asghar Khan.