Gen. Mohammed Zia ul-Haq, the president of Pakistan, made a few gestures in advance of his official visit here.

He didn't really have to as far as President Reagan is concerned. Zia was doubtless playing to Congress when, after months of delay, he allowed the widow of Zulfiqar Ali Bhutto -- the predecessor he deposed and executed -- to seek treatment for cancer in the West.

Nor did he, for Reagan's sake, have to release five of the dozen opposition leaders whom he arrested last week for making critical statements about his U.S. trip.

Zia knew, from the red-carpet reception accorded President Marcos of the Philippines, who also jails and executes his opponents, that Reagan has an exceptionally high tolerance for human rights violators.

If there had been any doubt in Zia's mind, it should have been resolved by Reagan's weekend performance during which he embraced the murderous leader of Guatemala, Gen. Efrain Rios Montt.

Amnesty International, America Watch and other human rights organizations have attested and documented the slaughter of thousands of peasants and Indians since the general seized power last March.

But Reagan, having looked him in the eye and studied the charts the general brought with him, is convinced that the Great Exterminator is getting "a bum rap." After their meeting, Reagan declared that his visitor is "totally dedicated to democracy in Guatemala" and deserves more U.S. military aid.

Rios Montt expressed his political philosophy in more robust terms: "We have no scorched-earth policy. We have a policy of scorched communists."

Nonetheless, Zia, who makes much of "mutual" U.S.-Pakistan "strategic interests," thought it politic, before setting out, to say that elections, which he has been promising and postponing since he took power 5 1/2 years ago, might not be the worst thing that could happen to his country.

For some members of Congress, who remember that Zia looked on while his countrymen burned down our embassy three years ago, the fact that Pakistan is on the border of Afghanistan is not the beginning and the end of the question. Sen. Mark O. Hatfield (R-Ore.), for instance, would like Zia to explain his policy of jailing his critics, without charges, and subjecting them to military trials that employ summary judgment procedures for which there is no appeal.

According to Amnesty International, the human rights situation has deteriorated markedly, with political imprisonment and torture on the rise.

Congress would also like to question Zia about his surreptitious development of nuclear weaponry. They are not convinced that the $3.2 billion in military aid Reagan proposes to bestow on him during the next six years will necessarily be used in the interests of the United States.

India is dubious about the sale of 40 F16s equipped with electronic countermeasure equipment, although Zia recently stopped in for lunch and a little stroking session with Prime Minister Indira Gandhi.

Some senators want to ask him specifically about the case of Irshad Rao, editor of a pro-Bhutto newspaper, who has been in jail and maltreated for almost two years for "printing objectional literature, creating unrest among the masses and disaffection with the armed forces."

Zia's transgressions were overlooked even by the pro-human rights Carter administration when the Soviets marched into Afghanistan two years ago. The visit to the Reagan White House gives him full "allied status"--which to Hatfield shows that "we are prepared to abandon everything to our consuming and myopic anti-Sovietism."

Zia can play the communist card with Reagan. He attended Leonid Brezhnev's funeral and met with Yuri Andropov. Pakistan is a member of a U.N. commission on Afghanistan. Reagan could urge him to help find a solution through a face-saving Soviet exit.

But perhaps the best thing Reagan and Zia could do is to watch the new British film, "Gandhi," together. It is a work of dumbfounding excellence.

Reagan, who consorts with bullies and views military action as the only way to stop "international terrorism," his term for communism, would greatly benefit from watching the uses of non-violence. It would do him good, in the light of his Latin American policies, to hear Gandhi saying that people would rather have a bad government of their own than a good government imposed by an alien power.

As for Gen. Zia, who, like his soul brother, Gen. Rios Montt, believes that political activity is murder, he needs all the instruction he can get in the art of benevolent leadership.

Sir Richard Attenborough, the producer and director, could doubtless arrange a screening of "Gandhi" for the pair. It's the kind of "quiet diplomacy" that might make a difference.