Heightened concern about nuclear proliferation has impelled the United States to seek new ways of curbing the spread of materials and technology that could be used to build atomic weapons.
In recent weeks, the US has called a meeting of Western countries that supply nuclear technology (the first such meeting in seven years) to talk about tightening controls, privately warned Pakistan not to build nuclear weapons, and agreed to meet with the Soviet Union on the subject. Secretary of State George P. Shultz is scheduled to give a speech on nuclear proliferation tomorrow.
Two new investigative efforts explain this increased concern and activity. The Congressional Research Service (CRS) reported over the weekend that, while no country outside the ''nuclear club'' (the US, Soviet Union, China, Britain, and France) has exploded a nuclear device since India did so in 1974, ''many states have or are acquiring a nuclear industrial base which they might use to produce nuclear weapons.'' This includes the ability to highly enrich uranium and plutonium.
Of the 23 countries studied by the CRS, five were cited as posing the greatest ''proliferation threat'': Israel, South Africa, India, Argentina, and Pakistan.
Another study, released yesterday by the Carnegie Endowment for International Peace, warns that in the past year the eight emerging nuclear weapons nations (the above five plus Libya, Iraq, and Brazil) ''took important steps toward building or expanding nuclear weapons capabilities.''
US officials are particularly worried about Pakistan, which may be getting help in developing its nuclear weapons potential from neighboring China. This concern was behind President Reagan's recent personal letter to President Muhammad Zia ul-Haq warning that nuclear weapons development could undermine US-Pakistani relations, especially the six-year $3.2 billion US aid program that includes modern conventional arms.
For the same reason, the Reagan administration has also held off submitting to Congress a plan to work more closely with Peking on nuclear energy matters that could relate to weapons production. The nuclear cooperation agreement was a key achievement when Mr. Reagan visited China earlier this year.
There is a political flavor to this, as well as to the agreement to meet with the Soviets on nuclear proliferation. Some analysts believe that progress in this area could be the back door to control of nuclear weapons, where US-Soviet negotiations now lie dormant.
Recently the administration has come under sharp criticism from environmental and other groups that charge that there has been ''a serious erosion'' of the steps taken by the Ford and Carter administrations to curb nuclear proliferation. For example, Reagan reinstated the military aid to Pakistan that Jimmy Carter had halted. The current administration, critics charge, has also been more willing to aid nuclear energy programs abroad.
Other experts say there has been considerable continuity between the Reagan administration and its predecessors on nuclear nonproliferation.
''Most of the substance of what Carter was doing is there,'' said Leonard S. Spector, author of the new Carnegie Endowment book and a former Senate staff member, who helped draft the Nuclear Non-Proliferation Act of 1978. ''There has been some erosion around the edges, but the bulk of it is there.''
Mr. Spector also said ''the role of the Soviet Union has been by and large extremely positive,'' both in working with the United States and in requiring (for the most part) that countries to which it gives nuclear energy assistance adhere to the 1968 Nuclear Non-Proliferation Treaty.
''Pakistan appears to have reached the nuclear weapons zone without testing, '' Spector said in a press briefing. ''They are very, very close, indeed.'' He also said that India is acquiring a significant plutonium-production capability, ''far above their energy power needs.''
He said that Argentina and Brazil appear to be in an ''infrastructure race ... but so far, at least, they are well away from producing nuclear weapons.''
''One of the most troubling stories to come to light,'' Spector said, was the recent indictment in Italy of suspects alleged to be part of a smuggling ring conspiring to ship weapons-grade plutonium to Iraq. In 1981, Israel bombed an Iraqi research reactor suspected of potentially aiding atomic weapons production.