Former Pakistani prime minister Zulfiqar Ali Bhutto, executed one year ago Friday, remains as much a thorn in the side of the martial-law rule of Mohammed Zia ul-Haq today as he was while he was still alive.

He has become a true martyr, deified in death by people who have forgotten how he manipulated the political system and mismanaged the economy, bringing about many of the problems that Pakistan now faces.

As a result, according to diplomats here and in Pakistan and Pakistanis interviewed over the past month, Bhutto's supporters form the most potent civilian political force in the country despite Zia's 5 1/2-month old ban on political activity.

Bhutto's widow, Nusrat, and his daughter Benazir have been given court permission over the objection of local authorities to pay a nighttime anniversary visit to the gravesite near the family home of Lakarna. The military government said it feared mass demonstrations.

Officials of Bhutto's Pakistan Peoples' Party have threatened to mass 100,000 persons in Lakarna Friday for the anniversary. According to reports reaching here, the isolated village in central Pakistan, about a six-hour drive from the seaport of Karachi, resembles an armed camp, full of Army and security officials determined to contain any demonstrations.

Most observers -- Pakistani as well as diplomats -- do not expect a mass demonstration for the anniversary.

Nonetheless, the force of Bhutto still dominates Pakistani politics.

Many observers believe that his execution -- after a trial, conviction and lengthy appeals on charges of conspiring to kill a political enemy -- changed the ground rules of Pakistani politics.

Never before had a leader ousted in a coup, as Bhutto was, ever been made to face, charges or been executed. Previously, changes in government, even sudden ones, had been gentlemanly affairs, with the ousted leader allowed to quietly live out his days in comfort, albeit without power.

After hanging Bhutto, many observers believe that Zia must cling to power to save his own neck.

"His remaining in office is a matter of personal survival now. I do not believe he can step down," said one experienced observer of Pakistani politics. Another suggested that Bhutto's hanging probably raised the premium on any life insurance policy Zia might buy.

Bhutto's death has also complicated Pakistan's relations with the oil-rich Arab nations that Zia now counts on to bail his country out of economic disaster and build up its military force to face the threat of Soviet troops on its northwestern border with Afghanistan.

Bhutto was a favorite with the Arab leaders, and Saudi Arabia's King Khalid was one of a vast number of world leaders, including President Carter, to plea to Zia for clemency for Bhutto.

As a result, the Saudi leaders are reported to have cooled to Zia and to have held back on some promised aid to Pakistan.

Since Zia recently rejected $400 million in U.S. military and economic aid, he must depend on the Saudis and his other Islamic friends to come across with the money to modernize his outdated Army.

That money is needed also to keep his fellow generals happy. For although Bhutto's party is the most powerful of the civilian political parties, Pakistanis describe the Army as the country's only meaningful political force.

The Army, too, has a stake in retaining power, analysts believe, because if the Pakistan People's Party takes over, most of the top military leadership will be out of jobs.

"If the Army decides it has had enough of Zia and can come up with an alternative," one well-informed diplomat said, "Zia is out.He has no resources to play against that kind of move."

"Short of an assassin's bullet he's not going to step down," the diplomat said. It can only happen by another general or a group of generals acting against him."

Gen. Zia, then, appears to be spending more time holding power and less time running the country.

"More than ever," said one diplomat, "he seems to have no formula for ruling. It's a day-to-day operation."

According to observers, Zia has developed no personal following in the 32 months since he overthrew Bhutto. At national day ceremonies last month, according to reports reaching here, Zia received only perfractory applause.

The traditional political leaders all oppose him since his technique has been to divide and weaken them.

While his emphasis on Islamization of Pakistan is not as unpopular among the masses as many Westerners think, it still causes grumbling among the educated classes.

"If he wanted a mullah," one Pakistani said, "we could have hired him for $50 a month. We didn't need to make him president."

It is questionable, however, whether Bhutto's party could capitalize on its executed leader's apparent popularity -- even if the Army let it.

Bhutto, a charismatic but arrogant leader, always kept the party as his personal instrument and continually cut down anyone he thought might challenge him.

That legacy, which may end up being Bhutto's greatest disservice to Pakistan, prevents any effective civilian challenge to the Army's rule.