Former prime minister Zulfiqar Ali Bhutto ended a week of tense speculation yesterday by announcing through his lawyer that he would, afterall, appeal his death sentence.

The appeal will be filed today at the very end of a seven-day deadline fixed by the Lahore High Court when it found Bhutto and four others guilty of conspiracy in a 1974 political murder case, and sentenced them to be hanged.

The case will now go to the Pakistan Supreme Court in Rawalpindi, and could be disposed of in as little as four weeks. Normally, cases sent to the seven-man court take up to two years to process, but it is believed that the court has already arranged that no other business will be conducted between April 10 and 25, leading to speculation that only the Bhutto case will be considered during this two-week period.

Meanwhile, the finance minister who served under Bhutto was arrested yesterday, according to a military government announcement.

Mubashir Hassan, who also was a founding member of Bhutto's Pakistan People's Party, was jailed in Kot Lakhpat prison, 12 miles from Lahore, on unspecified charges.

The announcement said police were also searching for Sheikh Rashid, former agriculture minister under Bhutto and People's Party vice president, but party sources said they believed he had gone underground.

More than 900 supporters of the controversial former prime minister have been arrested in the past three weeks.

Mrs. Bhutto, in a letter released by the family lawyer yesterday, accused the Pakistan military government of hatching a plot to poison her husband in his prison cell. She charged that the government was trying to give the impression to the world at large that the former prime minister was now a "broken man" so his death in his cell would be construed as suicide. A government spokesman late last night termed her charges "so preposterous as not to merit serious comment."

News of Bhutto's appeal will in all probability put a damper, at least temporarily, on the scattered outbreaks of violence that followed last Saturday's announcement of the death sentence.

At the same time, it is clear that Bhutto delayed announcing his appeal until the last practical moment to give time for an impressive campaign in opposition to the sentence to develop.

The relative lack of violence during the past week, however, may well spur on the military government in its determination to put Bhutto out of circulation.

It sems unlikely that Bhutto will fare well before the Supreme Court. The chief justice, Anwar Ul-haq, an Oxford-educated lawyer, is known to be personally opposed to Bhutto, who once ordered him passed over for promotion.

Gen. Zia saw to it that he was elevated to chief justice last year and that the Bhutto appointee to the job was retired.

Since Zia and reportedly twelve major-generals in the martial law high command want Bhuto hanged, it seems fair to speculate that the court - after a close examination of the case to be made largely for cosmetic reasons - will uphold the death sentence.

Zia made it clear in an interview this week, that he would not, under any circumstances, intervene after that decision.