The imprisoned political opponents of Pakistan Prime Minister Zuliqar Ali Bhutto indicated tonight that they may be willing to allow him to remain in office for a short period until new national elections are held.

The tenuous concession appears to be hinged on the opposition holding a controlling number of ministries in a caretaker government.

The concession, which has not yet been given final approval by the leaders of the nine-party Pakistan national Alliance, would go a long way toward defusing the explosive conflict that has been raging in Pakistan for the last seven weeks.

Since the March 7 national elections, which the opposition claims were rigged overwhelmingly in Bhutto's favor, the National Alliance has insisted on Bhutto's resignation.

Tonight, following an eight-hour meeting of all principal opposition leaders at a police guest house, acting Alliance leader Pir Sahib Pagaro told reporters that Bhutto had begun to approach the opposition's demands.

"His previous proposals were not worth considering," the pir said. "Now, we are considering because his new proposals are different. He is coming closer to our point of view. So we must make an effort to move closer to his."

Bhutto, who held an unsheduled meeting with members of his party at the National Assembly building in Islamabad late tonight, told Pakistani newsmen that he had no new offers to make to the opposition.

Sources within the opposition said that Bhutto has offered to hold concurrent provincial and national elections. This is considered an important advance over his original offer to hold only provincial elections and then if the opposition won clear majorities in all four of Pakistan's provinces, scheduling a fresh nationwide vote.

Bhutto has not admitted that he met last Saturday with the jailed president of the Alliance, Mufti Mahmoud, or that he offered to schedule concurrent provincial and national elections, as the opposition source indicated. The prime minister is considered by enemies as well as supporters to be a cunning political strategist and may be waiting for the opposition to tip its hand.

A caretaker with a majority of ministers from the opposition would cripple Bhutto until the elections were held and the Alliance presumably would use this interim period to strenghten its position.

Meanwhile, Bhutto's capacity to do battle with the opposition, in the streets of Pakistani cities as well as across a negotiating table, was markedly enhanced tonight by a pledge of allegiance by the joint chiefs of the 50,000-man armed forces.

The chiefs of the three armed forces and the chairman of the joint chiefs of staff said that while they deplored the imposition of martial law in three major cities last week, "we wish to make it absolutely clear that the Pakistan army, navy and air force are totally united to discharge their constitutional obligations in support of the present legally constituted government."

The statement was obviously intended to dispel widespread rumors of a split in the armed forces between the top leadership, all hand-picked by Bhutto, and junior officers and tropps who have been charged with implementing martial law.

The chiefs made their statement shortly after retired Gen. Tikka Khan, who commanded the Pakistan army during the bloody Bangladesh independence war in 1971, was sworn in as minister of state for defense and national security. Tikka is firmly in Bhutto's camp.

Despite its seeming willingness to compromise with Bhutto, the opposition has not changed its plans to stage a mass protest march on Bhutto's or some other time - if they consider such a show of strength necessary.

The PIR told reporters that the opposition had no intention of "causing unnecessary trouble, unless we're forced."