Islamabad: Bowing to the inevitable, President Yahya Khan announced early this week the indefinite postponement of the March 3 national assembly meeting which was to begin drafting the constitution enabling return to civilian rule. He did so "with a heavy heart", faced by the prospect of a strike "from the Khyber Pass . . . to Karachi" - threatened by PPP (Pakistan People's Party) Chairman Zulfikar Ali Bhutto - if the meeting went forward; and a general strike and riots throughout East Pakistan if it did not.

Yahya is playing for time - but it is doubtful whether time can heal the political rifts between the two main leaders. It is certain only that nothing else will. He has spoken of the need for more reasonable understanding of the issues of constitution-making; but the schism is real, and the arguments are not of a nature to be papered over effectively with limited concessions. Increasingly it is thought that Bhutto's announcement that his party would boycott the conference was fatal to the chances of accommodation - since it in effect forced Mujib publicly to reiterate at a vital moment that he would not jeopardise his plans for a near-independent "Bangla" nation.

The exchanges leading up to the decision for postponement were verbally colourful: Bhutto claimed forming a constitution without PPP participation "would he like staging Hamlet without the Prince of Denmark" - and less poetically threatened to break the bones of any assemblyman from a western party who went to Dacca. Mujib told his followers "the conspiracy against Bangla Desh has not yet ended" and that they would require "more blood to achieve our rights".

Superficially, there were hints of compromise in the past two weeks. The PPP convention agreed on a five- point formula which claimed to go some way to bridging the gap but which only served to emphasise it. Its "irreducible minimum" demands included a "truly" federal form of government with equal representation for each federating unit and a bicameral legislature at the centre to co-ordinate their planning and policy. It insists on a "fair arrangement" in respect of currency and taxation - while directly opposes Mujib's scheme to divorce taxation from the Jurisdiction of the central government - and further insists on the federal government's right to raise revenues to meet expenditure for "a minimum but viable centre". And it insists that the federal government control foreign aid and trade.

Though Mujib sees "no danger to the integrity of Pakistan if the constitution is framed on the basis of the six points", Bhutto's formula undoubtedly offers a better guarantee for the maintenance of the country's unity. But his hotheadedness in going for boycott tactics may prove to have been a key factor in tearing it apart. And to cap it, he warned that if new elections were called to break the deadlock over the constitution, his party would not participate.

Following the dissolution of his civilian cabinet and meetings with provincial administrators, Yahya flew to Karachi at the end of the month for last minute talks with Bhutto. His principal staff officer, Lieutenant General Pirzada, went to Karachi and Dacca in turn for talks with both sides. Mass protest movements appeared likely in West Pakistan's prosperous Punjab and Sind states if Bhutto did not get his way. But in Dacca too the position was stiffening.

The Awami League's parliamentary board went ahead with preparations for the assembly (and nominations for the seven seats reserved for East Pakistani women), while on February 28 Mujib announced that his constitutional formula belonged to the people and that he had no power to amend it. Rumours that he might consider adding foreign aid to defence, foreign relations and possibly - currency as central government concerns were stillborn. His price was said to be situating the capital in Dacca permanently (as opposed to six months in each year); but this seemed a small one for relinquishing provincial control of foreign aid, which had been strongly emphasised in the election campaign. Yahya's stipulation that a new constitution must be framed within 120 days of the first sitting of the constituent assembly made its postponement almost inevitable, with the two sides so far apart. Its wisdom is increasingly obvious - but as things are shaping, it begins to look almost like a tacit admission that there is no real alternative to martial rule, except the division of the country - which he has also vetoed. In spite of the tactical folly of Bhutto's move, it has not altered the vital question at all: will - and can - Mujib compromise on the election promises which went far to gain him his almost total control of East Pakistan's quota of seats?

Today's dilemma has been clearly mirrored in developments dating from well before the election, only brought into clearer focus by the magnitude of the Sheikh's win. It has always been extremely doubtful whether Yahya could be brought to consider Mujib's programme as compatible with national unity; without his blessing, prospects of civilian rule would be back to square one, with the constitution not approved and new elections scheduled. But if Mujib tempered his demands to meet political realities, could he hold the electorate? Mass violence in the East is never far away, and there are many more extreme voices with political carrying power - if Mujib loses the people's emotional mandate.

Immediately after the postponement announcement, it was hard to tell whether Mujib was running with the tide or directing it. With the streets of Dacca in chaos, he called for a total general strike which would probably have happened anyway. Shops shut up, cars disappeared from the streets and factories and businesses ground to a halt rather in response to angry and often armed crowds than to any single voice. Islamabad replied by imposing a curfew on Dacca; train and air services to the city were suspended.

A ban was placed on publication of material "detrimental" to unity or sovereignty; Wednesday Yahya, hoping to set a new date for the assembly's opening, called leaders to a conference on March 10. Bhutto accepted - but Mujib, who had earlier said he was ready to talk, refused. He said the invitation was "made at gunpoint" and called for civil disobedience in East Pakistan until government was handed to the people.