A Pakistani Foreign Ministry spokesman today angrily rejected U.S. charges that Pakistan is secretly working toward the capability to produce nuclear weapons.

The spokesman said the U.S. decision Friday to cut off economic and military aid to Pakistan was an act of discrimination provoked by "Zionist circles" who want to prevent nuclear research by Islamic states.

The spokesman refused, however, to respond to reporters' specific questions about the gas centrifuge plant for the enrichment of uranium that the United States believes is being built in Pakistan.

"We have a research program in the peaceful uses of nuclear energy." the spokesman said. "Why don't you go and ask your own government about its germ warfare plants" Why not ask them about their nuclear bombs" It Pakistan the only country which is engaged in research for various methods of producing nuclear energy?"

The United States has been piecing together information showing that Pakistan has been surreptitiously buying pieces of equipment to make up a gas centrifuge enrichment facility. European "front" companies allegedly have been used in some cases.

Pakistan has no peaceful use for enriched uranium.

The American belief is that Pakistan's military ruler, Gen. Mohammed Zia ul-Haq, is determined to equip his country with a nuclear bomb which will match the proven capabilities of neighboring India.

There are also fears that Pakistan's nuclear program is being aided by some Arab countries-Libya is specifically mentioned-and that once scientists here have perfected the technology, its results will be handed over to other Islamic countries.

The Foreign Affairs spokesman here "summarily rejected as false" these charges.

"Somehow, Islam is disapproved of and it gives more concern if an islamic country carries out research into some nuclear technology than if other countries of the world do so," the spokesman declared.

"There are people in the States who say that if Pakistan gets te bomb it will be passed to the Arabs, the Palestine Liberation Organization and Col. Qaddafi (of Libya), and then it will be used against Israel.

"Zionist circles, Israeli circles, and therefore American circles are obsessed. They say, 'You will get the bomb and give it to the Arabs. It will be horrible.'"

It is understood here that a series of blunt warnings were given to Pakistani officials, from Gen. Zia down, but that the Americans failed to get a straight answer to questions about the construction of a gas centrifuge plant.

The U.S. Ambassador, Arthur W. Hummel Jr., arrived back today after five weeks of consultation in Washington. Hummel is to seek an early meeting with Gen. Zia, in an attempt to ensure that the aid cutoff does not harm other aspects of U.S. Pakistani relations. About $85 million in economic and military aid is affected, but $40 million in food aid will continue.

For its part, Pakistan is also anxious that there should be no undue souring of relations.

A Pakistani statement tonight "categorically denied" that the country's "peaceful nuclear program" had behind it the intent or purpose of developing a nuclear bomb. However, observers noted the careful use of the words "peaceful nuclear program" and pointed out that this did not rule out the existence of a separate military program.

The Foreign Office spokesman said Pakistan was ready to accept full safeguards to cover its "peaceful program of nuclear research" provided these were not discriminatory. In other words, the United States would have to ensure that the safeguards were applied to every other country, he added, including Israel, India and South Africa.

U.S. fears that Pakistan's program to build a bomb-and with a uranium enrichment process, this could take up to seven years-will provide more muscle to the Indian nuclear lobby which is agitating for the construction and development of nuclear weapons.

India exploded a device in May 1974, but Washington beleives that, at the moment, it has no nuclear bombs ready on the shelf. However, India does have a nuclear reprocessing plant which produces plutonium, and this gives it the capability of constructing bomb within a few months. CAPTION: Picture, MOHAMMED ZIA UL-HAQ . . . warned by U.S.