President Mohammed Zia ul-Haq insisted today that any U.S. military help to bolster Pakistan's defenses against Soviet troops on its border must be coupled with long-term economic aid.

"Pakistan is in need of assistance to modernize and strengthen its defense forces. But more than that, Pakistan ought to stand on very durable economic ground. I think that aspect ought to be involved," Zia told a press conference after a day of meeting residents of this provincial capital in the shadow of the Khyber Pass, with Soviet troops just 36 miles away in Afghanistan.

Government officials said Pakistan wants long-term economic aid as well as arms.

"Military aid without economic aid is unexpendable," said one, reflecting Zia's view.

In Washington, Carter administration sources disclosed that the president has tentatively approved $400 million in U.S. military and economic aid to Pakistan beginning immediately, if Congress consents, the Associated Press reported.

All the weapons would be "defensive" and warplanes would be excluded in deference to India's concern about strengthening Pakistan, its neighbor and traditional rival, the AP said.

[Former secretary of state Henry A. Kissinger called for the United States to discuss with Pakistan establishing air and naval bases there. Story, page A5.]

Zia underscored the current Pakistani stance of playing hard to get on accepting U.S. military aid, which President Carter has said is a cornerstone of American response to the Soviet movement of troops into Afghanistan.

But Zia and other officials and diplomats said that Carter's public statement was not preceded by consultations. Some Pakistani diplomats said Carter's public offer embrassed the country.

Zia said Pakistani forces on the border have "taken some defensive measures" to meet the threat of the estimated 85,000 Soviet troops in Afghanistan, but it was obvious that this frontier Army garrison has not gone on a war footing.

"There is no war in Pakistan. We do not want to create a war phobia," said Zia. He repeated the frequent Pakistani complaint that the U.S. has been an unfaithful ally, letting down Pakistan during its 1965 and 1971 wars with India.

In effect, Zia called for a return to the halcyon days of the 1950s, when Pakistan was a major recipient of American military and economic aid and was considered a principal Asian ally. The U2 spy flights over the Soviet Union were run from an air base in the city.

Now, Zia said, the United States is going to have to prove its "credibility and durability" as an ally before Pakistan will take aid. "I hope these two words will make my position clear," he said, refusing to elaborate on what he expected the United States to do to prove itself faithful in Pakistan's eyes.

Pakistan clearly is taking advantage of being in the position to protect the West against Soviet expansion toward the Persian Gulf.

"It is time the world should know what the reality is in this part of the world," Zia told the press conference.

In face Pakistan is now a focus of world attention. British Foreign Secretary Lord Carrington arrives Monday for a two-day visit centered around talks with Zia about the possibility of a Western consortium providing arms to Pakistan.

Later this month, an Islamic foreign ministers' conference is to be held in Islamabad, the Pakistani capital, to discuss the Soviet invasion of Moslem Afghanistan and possible aid to rebelling tribesmen fighting under the banner of Islam against "godless communism."

Zia's foreign policy adviser, Agha Shahi, discussed U.S. aid to Pakistan with Secretary of State Cyrus Vance in Washington in recent days. Zia said he no details of the meetings, but added: "I think we have been able to reach some understandings."

U.S. relations with Pakistan became strained last April when President Carter cut off aid because of the conviction among American officials that Pakistan was clandestinely starting an atomic weapons program -- a charge that Zia denied again today.

Relations worsened six weeks ago, when Zia's government failed to stop a mob of Pakistanis from burning the U.S. Embassy with 90 persons trapped inside. Two Americans were killed.

While Zia said today he was willing to "start with a clean slate," Pakistani officials have made clear in private talks with reporters that this country will not stop its nuclear program as a condition for U.S. aid.

Zia said Pakistan has been holding close consultantions with China about the Soviet military move into Afghanistan -- an indication that it expects added military aid from that nation.

Some government officials have referred to China as a faithful ally that has bolstered Pakistan's military capability during the past decade, while America let it down. But diplomats in Islamabad have noted that the weapons China has supplied this country are no match for the sophisticated Soviet equipment in Afghanistan.

Zia today ruled out any Pakistani military aid to the Afghan rebel fighters and told a meeting of tribal chiefs, many of whose relatives live in Afghanistan, that this was not the time for a holy war against the Soviet troops there.

Yusaf Khan, one of the chiefs from the Mohamand tribe, said his fellow chiefs "are not very much happy about the president not allowing the holy war. We 100 percent believe that if you fight and die you go to paradise so why should we not fight and die for the country?"

Zia promised continued help for the Afghan refugees, who have poured over the border into Pakistan in increasing numbers since the Marixists sized control of Afghanistan in April 1978.

There are estimated to be more than 400,000 refugees in Pakistan, with 20,000 arriving in the two weeks since Soviet troops moved into Afghanistan in force. Zia predicted the number will quickly rise to a million.

He said international aid for the refugees has been "a drop in the ocean," with Pakistan paying 160,000 a day to feed and clothe them. "That isn't a very minor amount for a country like Pakistan, which hasn't very substantial resources of its own."