Tightened security measures were in force throughout Pakistan today as the sentencing to death of former Prime Minister Zulfiqar Ali Bhutto for conspiracy in a 1974 political murder pushed the atmosphere in the country once again to a tense, even sinister pitch.

Only two minor pro-Bhutto demonstrations by students in the cities of Hyderabad and Dadu were reported. But the tension underneath the outward calm in major cities, was unmistakable, a feeling added to by the presence on main streets of hundreds of police equipped with rifles and riot sticks.

Bhutto and four ex-security agents in his government, ousted in a bloodless military coup last July 5, were sentenced early yesterday morning by the Lahore High Court "to be hanged by the neck till they are dead," after being found guilty of hatching a plot to assassinate a political foe.

The case four-month-long trial without jury stemmed from the November 1974 killing of the father of one of Bhutto's most implacable political enemies, Ahmad Raza Kasuri. A group of gunmen who the government said were working for one of the Bhutto governments's security agencies fired on Kasuri's car as it drove from a wedding party in a Lahore suburb. Kasuri himself was unharmed but his father, Mohammed Ahmed Khan, was hit by three bullets and died later in hospital.

Bhutto, who pleaded not guilty to charges that he ordered the attack, yesterday decided not to appeal against the sentence and his lawyers were working frantically to try to persuade him to change his mind.

They were hampered by being denied full access to their client, who is under heavy guard in a small country prison near here.

A close family friend said: "This is so characteristic of his pride. He would rather go down in history as a great martyr than to go crawling to a regime for which he has no respect."

The President of the Lahore branch of Bhutto's Pakistan People's Party, warned that "the people of Pakistan will not stand idly by if their former leader is hanged, as the unanimous court judgment ordered. "There can be no doubt that they will take to the streets in support of him," Arifiqbal Bhatti said. "There is still a great feeling in the country for him."

For Pakistan's military ruler, Gen. Zia ul-Hag, the next few days will be crucial. He has done everything possible to forestall a popular outburst. The Bhutto family is under strict house arrest, political activity has been totally banned, hundreds of members of the People's Party have been locked up in prison (though certainly many fewer than the 93,000 alleged by the party itself to have been detained.)

The press is being more severely censored than usual and public comentary on the trial verdict has been officially discouraged. And, apart from the police, the military is on full alert in case of trouble, with orders to hit hard at any unrest in the cities.

If the week - which includes the Pakistan national day Thursday - passes without incident, there will be pressure from Zia's more hawkish colleagues to see that Bhutto hangs. The very fact of his continued presence here poses an ever-present threat to the Zia regime. Yet, at the same time, Arab pressure to spare Bhutto, who has many frineds among the Persian Gulf states and North African leaders, will give Zia cause for second thoughts.

Judgement in the extremely sensitive case was delayed for at least a week after the intervention by several Arab countries whose leaders were friendly with the Bhutto regime. It is known that representations had been made to Zia by the Libyan, Iranian and Saudi Arabian missions in Islamabad, Pakistan's capital.