KARACHI, PAKISTAN, JULY 15 -- President Mohammed Zia ul-Haq today linked two massive terrorist bombings that killed at least 72 here last night to agents opposed to Pakistan's support for Afghan guerrillas fighting against the Kabul regime and Soviet forces there.

Business and government life came to a halt in reaction to the bombings, which also left 140 hospitalized, including 15 listed in critical condition tonight.

Zia, who flew to Karachi today from Islamabad, was able to visit survivors in only one of two major hospitals because angry students were demonstrating at the other.

At a press conference, Zia faced hostile questions from reporters about Pakistan's role in the nine-year-old Afghan war. There were also angry protests across the city against the presence of more than 3 million Afghan refugees in Pakistan and the government's inability to stop terrorist bombings apparently orchestrated by Kabul.

Police had to use tear gas at the Civil Hospital during the early morning hours when doctors and medical students besieged the Sind provincial chief minister and governor, who were trying to visit survivors.

"It is the beginning," Zia said at a press conference today, referring to the bombing. "I want the people of Pakistan to be more courageous. We have to face it {terrorism} and launch our war against it."

One man was killed during a violent demonstration at the Liaqatabad police station in West Karachi. Police said he was hit by gunfire from the demonstrators, but witnesses said it was the police who opened fire.

The two powerful car bombs yesterday exploded 20 minutes apart at busy downtown sites during the evening rush hour.

The bombs were the most devastating of a series of such attacks that have shaken Pakistan's other major cities -- Lahore, Peshawar and Rawalpindi-Islamabad -- in recent months. The government has blamed them on the secret police of neighboring, Soviet-dominated Afghanistan. There have been no statements by Kabul.

{In Washington, State Department spokesman Charles Redman said "the most one can do now is look at previous similar incidents . . . and if that's any indication, then this would appear to be the work of agents operating under the control of the Kabul regime's secret police."}

Previously, such incidents were limited to the Peshawar area near the Pakistan-Afghan border, where many of the refugees live and guerrillas come for safe haven when not fighting. As the fighting inside Afghanistan has escalated, however, so have the terrorist bombings. There have been 13 bomb blasts across the country this year.

At the Civil Hospital this morning, students from a nearby medical college put up signs saying, "We won't let Zia in," and "The government can't protect us." Observers said students from both left-wing and right-wing organizations put up similar signs.

Zia, at his press conference, warned that the object of the bombings is "to split the people and the government."

"There is a very difficult time ahead," he said.

"Agents opposed to Pakistan's policy toward Afghanistan are the real culprits," Zia said. "These sabotage activities are directly aimed at forcing Pakistan to change its Afghanistan policy."

When pressed by one journalist, who linked the terrorist incidents to Pakistan's support for U.S. policy in Afghanistan and elsewhere in the region, Zia became animated, reflecting the sensitivity here to the growing links to Washington.

"Negative. Your statement is wrong," he said abruptly. "How can you say that? You first accept we are nonaligned and that we are not aligned to one superpower.

"Do you think I am a policeman for American interests here?" he asked. "The government of Pakistan will act only in the interest of Pakistan.

Pakistan's policies are nonaligned, absolutely nonaligned, Zia said."

The president indicated the government is seeking outside support in combating the terrorist actions.

"We are not just praying," he said. "We are seeking international cooperation. You will see the results soon."

U.S. bomb experts reportedly were called in to check the site of bombings earlier this month in Lahore.