Pakistani President Mohammed Zia ul-Haq said today that the Soviet Union and its Afghan ally have suffered 60,000-70,000 casualties in less than six years of warfare in Afghanistan and predicted that Moscow will conclude sooner or later that "there is no military solution."

Zia spoke in an hour-long interview that also covered his hopes for improved relations with Indian Prime Minister Rajiv Gandhi, whom he will meet at the United Nations here Wednesday. In addition, he discussed the more limited, nonmilitary role he sees for himself and the currently banned opposition parties when martial law is lifted by the end of the year.

The Pakistani leader, who addresses the U.N. General Assembly on Wednesday, also said that Benazir Bhutto, a leading figure of the main opposition Pakistan People's Party who has been under 90-day house arrest since late August, "can leave the country any time" and is expected to go back to France before Nov. 6. She had returned to Pakistan from France to attend her brother's funeral.

Zia expressed long-term hopes, but few short-range expectations, for the Afghan policy of the new Soviet leader, Mikhail Gorbachev. He depicted Gorbachev as taking a "wait and see" attitude toward the Afghan war while being preoccupied with internal questions.

Meeting Zia in Moscow as he took power last March, Gorbachev delivered a personal warning about what he charged was Pakistan's aid to the Afghan resistance. Zia said that in the seven months since that meeting, the Soviets have intensified both their military activity inside Afghanistan and their "border violations" on the Pakistani side of the Afghan-Pakistani line.

In the war zone, said Zia, the intensification of Soviet military activity in four offensives so far this year has caused higher casualties on all sides, but "it has not made much difference to the activities of the freedom fighters inside Afghanistan."

Discussing the military situation in Afghanistan, Zia, a career soldier who took power under martial law in 1977, said that although actual numbers are much smaller, the Soviets have suffered proportionately greater combat troop losses than did the United States in Vietnam or the allies in World War II.

The total toll of killed, wounded or sick among Soviets and their Afghan allies is 60,000 to 70,000 men, Zia said. State Department sources said these were credible estimates. The U.S. estimate early this year, before the stepped-up fighting, indicated that about 9,000 Soviets may have been killed and 16,000 wounded. Zia, saying "we have very close eyes" on the situation across the border, put the present Soviet force in Afghanistan at 150,000 men, which is substantially higher than the 115,000 to 120,000 estimated by the United States. He said there were no casualty figures for the antigovernment forces that could be authenticated.

Zia described violations of Pakistan's border, including bombing raids, as attempts "to intimidate people in the border area."

"These warnings cannot be ignored," he said, but gave no hint that Pakistan would change its course. "You've got to put up a fairly good poker face," Zia said of his response to Soviet pressures.

Soviet leader Yuri Andropov, who came to that post after being head of the KGB, or secret police, was reputed to be personally opposed to the Soviet occupation of Afghanistan. Zia said that "we saw definite signs" that Andropov as Kremlin leader had been "following a policy of leniency in trying to resolve the Afghan issue."

Gorbachev, on the other hand, was described by Zia as "not so much in a hurry" to find a resolution to the Afghan problem, "which in his Gorbachev's opinion, the military is tackling."

The new Soviet leader seems willing to "wait and see" whether an intensification of Soviet military action can change the situation to Moscow's advantage, according to the Pakistani.

Zia predicted with an air of considerable confidence that this effort will not succeed. He said that it was his impression Gorbachev is sensitive to the propaganda loss the Soviets suffer in much of the nonaligned world over Afghanistan and that "one day the Soviet Union will come to the conclusion that there is no military solution" and thus a diplomatic solution must be arranged.

Zia said that next month's summit meeting in Geneva of President Reagan and Gorbachev could have a "tremendous" positive effect on Moscow if the U.S. leader, with "the right perspective and the right emphasis," makes some simple but clear-cut points about Afghanistan.

Those points are, Zia said, that the Soviet Union must withdraw from Afghanistan and that it can leave behind a "friendly" and "nonaligned" Afghanistan, with no outside interference allowed by anyone, including Moscow.

Zia expressed some concern and surprise at the actions in the past six weeks of Gandhi, who has stepped up his accusations that Pakistan is building atomic weapons. Nevertheless, Zia spoke warmly of the new Indian leader as "an open-minded, simple, forthright person" and said he hopes his talks here with Gandhi help "remove the suspicions, misapprehensions and lack of confidence" between the neighboring countries.

He said he had apprehensions that India, which exploded a crude nuclear device in 1974, already had "some nuclear devices for military use" and that a newly operational plutonium-producing breeder reactor, which Zia described as operating without international safeguards, "must create a lot of fear and concern" in the region.

He said both countries could resolve their nuclear fears of each other with bilateral, regional or international accords but said, "I don't know if India is that keen to be bound" by such agreements.

Zia said that his government is asking for more than the current $3.2 billion in the next five-year program of U.S. military and economic aid to his country. The present program is about evenly split between military and economic help. But Zia said that next time he wants to increase the percentage going to economic help while adding "a little more" to the current $1.6 billion in military aid.

Zia reiterated his pledge to end martial law by the end of this year and said there were "all reasons" for it to end even sooner. He said that, for another five years, he would retain the presidency, with more limited powers than he presently wields. A new prime minister would be the chief executive. Zia would end his military role as leader of the armed forces.

As a step toward lifting martial law, Zia pushed a new law through Pakistan's National Assembly last week that critics contend merely seeks to legitimize what was done under his martial-law rule and protect him from prosecution from some future government.

Another key bill that may allow opposition parties to operate freely once again, comes before the assembly next month. Under questioning today, Zia said, "I see no reason" why what he described as a "refined" version of the Pakistan Peoples' Party "should not function" once again. Zia said how "refined" the party becomes would depend on how party leaders controlled their various factions.

Before a party could be revived, however, it would have to register and be approved by an "independent" electoral commission. The parties would have to show their political manifesto, financial support and commitment to democracy. Zia described the commission as a device to import a "certain form of discipline" on the political process.