The United States and the major nuclear supplier nations are developing new international lists of high-technology equipment and materials that would be made subject to strict export controls because of their value to countries seeking to develop atomic weapons, according to diplomatic sources.

This two-year initiative by the Reagan administration, which officials refuse to discuss publicly for fear of jeopardizing its successful conclusion, is in marked contrast to previous administration retreats from some of President Carter's tough policies against proliferation of nuclear technology.

If at least tacitly accepted by all major supplier countries, these far-more-detailed lists, called "trigger lists," would bring the policies of several nations more in line with generally tighter U.S. nuclear export controls and would represent a major step toward common nonproliferation guidelines.

As an initial step, the sources said, a list has been compiled of 26 key items that would be needed by a country seeking to build an ultra-centrifuge enrichment plant, one of several types of facilities that can produce highly enriched uranium suitable for manufacturing atomic bombs.

This more-detailed list is designed to increase obstacles facing a country such as Pakistan, which for several years has been attempting to buy equipment needed to construct such a plant on a piecemeal basis and avoid international inspection.

The enhanced list, which the United States has been developing for more than two years through bilateral negotiations and two rounds of multilateral talks in London, was presented to the Nuclear Non-Proliferation Treaty Exporters Committee at a secret meeting in Vienna last November.

This committee, called the Zangger Committee because it is chaired by Swiss energy expert Claude Zangger, drew up in 1974 the first list of technologies that, because of their possible use in producing nuclear weapons, should trigger safeguards under the 1968 Nuclear Non-Proliferation Treaty.

The committee has 21 members, including Britain, West Germany, and the Soviet Union and several of its Eastern Bloc allies, but neither France nor China. France, however, is cooperating in the effort.

The nations that met in November agreed to hold another Zangger Committee meeting in Vienna late this month in an effort to resolve various technical and legal disputes, and U.S. experts hope that tentative agreement can be reached on further strengthening the ultra-centrifuge list.

Final agreement on the new list is not thought likely before late spring.

If this initial attempt to enhance earlier trigger lists succeeds, the participantsare expected to try to compile detailed lists of equipment needed for plutonium reprocessing plants and other sensitive nuclear facilities. Plutonium, like highly enriched uranium, can be used to make atomic weapons.

While the final ultra-centrifuge list probably will not be as comprehensive as U.S. experts would like, most nevertheless feel that this first effort to update and fill in gaps in earlier trigger lists represents a major step forward in the international effort to slow spread of sensitive nuclear facilities.

The new list would prevent a recurrence of contentions by several nations that they had no way of knowing that parts they exported to Pakistan were destined for use in its uranium enrichment plant.

"The problem with existing trigger listsis they are highly general and, for that reason, extremely difficult to apply, particularly by supplier countries that are not nuclear weapons states," a State Department official said.

"They say they do not know what kind of items could be useful to a country bent on developing a weapons program," the official said. "We are trying to redress that."

The initial Zangger trigger list, drawnup by supplier nations following India's 1974 underground nuclear test, was extremely vague. While it called for safeguards on uranium enrichment and plutonium reprocessing plants, which can produce materialusable in weapons, it did not bar their export.

But the following year, a smaller groupof supplier nations called the Nuclear Suppliers Group began meeting in London in an effort to reach agreement on a more restrictive list. This group, which became known as the "London Club," secretly adopted in 1976 a new set of "Guidelines for Nuclear Transfer."

These guidelines, and an expanded trigger list that emphasized tougher controls on export of uranium enrichment, plutonium reprocessing and heavy water plants, were published by the International Atomic Energy Agency in 1978.

While the earlier efforts of the Zangger Committee attracted little attention, Third World countries mounted a massive outcry against the "London Club," accusing the supplier states of undermining the Non-Proliferation Treaty by forming a cartel designed to perpetuate their lead in nuclear technology.

As a result, the administration has worked hard to keep secret what many view as one of its most important nonproliferation efforts, which has involved various Cabinet departments and agencies.

In an attempt to avoid the impression that these new controls are being imposed on the Third World by a small "club," the United States also has resisted the Soviet Union's suggestion that the new trigger list be adopted not by the Zangger Committee but by the smaller Nuclear Suppliers Group.

The administration's position is that the current effort is simply an update of the Zangger Committee's continuing responsibility to establish conditions for nuclear exports under Article 3 of the Non-Proliferation Treaty.

France, while a participant in the Nuclear Suppliers Group, is not participating formally in the Zangger Committee because it is not a signatory of the Non-Proliferation Treaty. But the United States and France have held bilateral talks on the new list, and France has indicated that it will adhere to any new guidelines generally adopted.

China is not a signatory to the Non-Proliferation Treaty and did not participate in formulation of any of the earlier trigger lists.

The draft list of ultra-centrifuge parts includes such items as electrical inverters, scoops and rotors. The United States is also seeking controls on the export of materials such as ultra-high-strength aluminum and maraging steels, nickel-iron alloys of extremely high strength.

Zangger Committee members are Australia, Austria, Belgium, Canada, Czechoslovakia, Denmark, Finland, West Germany, East Germany, Ireland, Italy, Japan, Luxembourg, the Netherlands, Norway, Poland, Sweden, Switzerland, Britain, the United States and the Soviet Union.