ISLAMABAD -- Pakistan's President Zia ul-Haq said he won't sign an Afghanistan peace accord with the current Afghan leader, Najibullah.

Zia's remarks, made in an interview last week in his spacious office here, are the clearest signal yet that Pakistan wants a new coalition government in place in Kabul before signing the so-called Geneva accords, the four-point peace plan that is being hammered out in secret talks between Pakistan and Afghanistan. The talks are expected to resume next month for what some observers had hoped would be a final round of bargaining.

"We cannot sign with Najibullah," said Zia. "How can a government of Pakistan sign the Geneva accords with the man appointed by the Soviet Union who is responsible for killing so many people?"

Zia also critcized Najibullah's party, the People's Democratic Party of Afghanistan (PDPA), and said indicated that he wouldn't sign a peace agreement with a new government dominated by the PDPA. Zia explained: "The present regime is Soviet-oriented. It cannot therefore be accepted . . . . How can you expect Pakistan to say this interim government should be formed by the PDPA? Is it wrong." He added: "The present regime cannot be given any permanent role, but all factions of Afghans must get together." Asked whether this coalition might include members of the PDPA, Zia said he might accept "some people who can represent their faction."

In his comments last week, Zia clarified his diplomatic goals in the Afghanistan negotiations. He also appeared to be taking a somewhat tougher line than he had in an interview earlier this month with The New York Times, when he indicated that he would support participation by members of the current pro-Soviet Afghan regime in a successor government. Those earlier remarks had surprised some Reagan administration officials.

In other remarks during the lengthy interview, Zia disclosed that:

China has been a major backer of the mujaheddin. "The Chinese support is as important as the U.S. support," Zia said.

An international peacekeeping force should supervise Soviet withdrawal from Afghanistan. "Pakistan believes there should be a peacekeeping force to ensure the monitoring of the Russian withdrawal," Zia said.

Zia's comments come at an especially delicate time in the negotiations. Three of the four points of the Geneva accords have already been agreed upon: the right of over three million Afghan refugees to return to their country; a cut-off of outside aid for the mujaheddin resistance fighters, and Soviet troop withdrawal. The main outstanding difference at present is the timetable for withdrawal of Soviet troops. At the last meeting in December, Pakistan stuck to eight months while Najibullah's regime insisted upon 16 months.

The talk here and in Kabul is that the timetable problem may be resolved at the next Geneva meeting, clearing the way for signing the accords. Najibullah said in an interview in Kabul a week ago that he would accept 12 months, and diplomats there said he would settle for 10. (Indeed, Afghan Foreign Minister Abdul Wakil said in an interview that less than 12 months might be acceptable to the Afghan regime.)

Who signs the accords could be an important factor in shaping a post-war Afghanistan. Zia's fear is that if Pakistan signs the accord with Najibullah, it will remove his pariah status and accord him de facto recognition. Since the mujaheddin claim to control 80 percent of the country, Zia hopes that they will similarly dominate the interim government.

President Zia said he would press Soviet deputy foreign minister Yuli Vorontsov on creation of an interim government when he visits Pakistan, probably later this month or in early February. Zia said he would urge the Soviet official (and the mujaheddin) to agree to the formation of an interim government that include the mujaheddin, the Afghan exiles, and perhaps some elements of Najibullah's People's Democratic Party of Afghanistan -- but not Najibullah himself. Zia's hope is that this interim government would then sign the Geneva accords with Pakistan.

"The mujaheddin have won the war," said Zia. "The Soviet Union has lost. It is only a question of not rubbing it in too hard. The Soviet Union wants a face-saving device, and the mujaheddin should offer it to them because the aim should be the vacating of Afghanistan by Soviet troops."

How to put together such an interim government is the subject of the day in Pakistan. According to senior officials, the idea has been under discussion for almost a year. This week President Zia, Prime Minister Mohammed Khan Junejo and other Pakistani officials met with Afghan resistance leaders to discuss the possibility of a coalition government in Afghanistan.

Mujaheddin leaders -- such as Yunis Khalis and Gulbadin Heckmatyr -- said last week in interviews that they steadfastly reject the sort of coalition Zia is proposing. But Pakistani officials claim that in private conversations, these resistance leaders are more flexible.

How would such an unlikely coalition be put together? Zia insists the Afghans should work it out themselves in a large meeting, and he offered Pakistan as the site for such a meeting. "I suggest a democratic process to form an interim government, and after the interim government, the democratic processes should be allowed to evolve," he said.

The Soviets have refused, thus far, to talk directly with the mujaheddin. Moreover, the mujaheddin have not been a party to the Geneva meetings -- which have been attended only by Pakistan and Afghanistan with a Soviet observer. But Zia disclosed one previously secret aspect of the Geneva accords when he said they call for U.N. mediator Diego Cordovez, "to assess from the refugees that the arrangements made are suitable to them. Without this, Geneva is not agreed upon," he said. (When Cordovez visited Pakistan last week, Khalis, the leader of the resistance alliance, refused to meet with him.

Zia denied that there is any split between the United States and Pakistan over the formation of an interim government. "The U.S. and Pakistan speak with one voice," he insisted. "We both believe this is a problem of the Afghans and they must resolve it themselves."

Zia hinted that despite his talk of coalitions, he remains skeptical of the prospects of complete Soviet withdrawal from Afghanistan. He's in a delicate position: with bombs planted by Afghan agents exploding all over Pakistan, with growing internal political pressure to settle the Afghanistan issue, and with a flurry of peace offers coming from the other side. With so much in the wind, Zia may wish to strike a conciliatory pose and at the same time test Soviet promises.

Pointing to a map of Afghanistan, Zia explained: "If you look at the advantages strategically, there is no reason they {the Soviets} should vacate. They've blocked China on the east, they encircled Iran, and they are 200 miles from the warm waters. They are sitting practically on the mouth of the Straits of Hormuz. Why should they give it up?"

Nevertheless, he concluded, we should test Gorbachev and see if he keeps his promise to withdraw in 1988. "If you take the indicators physically on the ground then there is nothing to show the Soviet Union means what it says." Yet he says he believes that Gorbachev wants to develop the Soviet Union economically and that therefore it would serve him well to be rid of the expense of Afghanistan. Moreover, Zia points out that the Soviets have lost over 35,000 men and 1,600 tanks as well as 1,000 aircraft.

"My gut reaction is we should believe Gorbachev because then there is the possibility that Soviet troops will leave Afghanistan," he said. "Let us take him on his word and see if he can pull off the miracle of the 20th century -- for the Soviets to withdraw and Afghanistan to be a free, independent and neutral state."

Lally Weymouth writes regularly about foreign affairs for The Washington Post.