President Reagan returned from China with an agreement on commercial nuclear cooperation in his pocket. But he will have to convince Congress that it is a good agreement before American firms can look forward to concrete business deals.
Concern is voiced in congressional circles and the arms control community that the President may not have obtained a sufficient guarantee from the Chinese not to help other nations make nuclear weapons. On this sensitive issue the administration is relying in part on Chinese oral assurances, including a statement made by Premier Zhao Ziyang in a White House dinner toast in January: ''We do not engage in nuclear proliferation ourselves, nor do we help other countries develop nuclear weapons.''
China has not been willing to write such language into an agreement, contending that this would infringe its national sovereignty. But administration officials say they are satisfied with Zhao's public statement as well as with conversations with the Chinese prior to that statement and similar assurances given to Australian Prime Minister Robert Hawke in Peking in February. They also point to the fact that China has joined the International Atomic Energy Agency.
''In the last year we have seen a major move by the Chinese to accept many of the most important norms and practices in the nonproliferation field,'' says an administration official. ''They have made clear to us that they will not assist other countries to make nuclear explosives, and that they will require safeguards on their nuclear exports. We now have a nonproliferation framework with China which permits nuclear cooperation.''
Moreover, the US official stresses, China has committed itself - in writing - not to use US-supplied nuclear material and equipment for anything other than peaceful purposes, and not to transfer to another country or reprocess such material without prior US consent. It has also agreed in writing to US ''visits'' to check implementation of the agreement.
''So we're not relying merely on oral statements,'' says the official. ''The Chinese have moved a long way.''
Under the US Nuclear Nonproliferation Act of 1978, China is not required to give a nonproliferation pledge. But if it did provide nuclear weapons aid to a third country, the President could cut off nuclear trade.
Lawmakers are reserving judgment on the initialed Sino-American agreement pending hearings later this month. While the State Department has briefed Senate and House staff members and communicated with some legislators, it has not yet released the text of the agreement, a fact that has drawn some criticism. According to congressional sources, the House Foreign Relations Committee, which will hold hearings May 22, has asked the administration for the text by that time.
''It's silly that they won't show it early, because there won't be any changes in the wording,'' says an aide to Sen. John Glenn (D) of Ohio, a strong advocate of nuclear nonproliferation. ''They just want to put Congress at a tactical disadvantage.''
The President has yet to sign the agreement. This happens only after various executive agencies, including the Departments of State and Energy, the Nuclear Regulatory Commission, and the Arms Control Disarmanent Agency, submit their views and recommendations. Once signed, the agreement is given to Congress where it must lie for 60 days of continuous session. It then goes into effect unless Congress specifically disapproves it.
Tough questions are expected to be asked about the agreement because of China's history on the issue. There is strong suspicion, for instance, that China has provided Pakistan with nuclear know-how on making an explosive device. Peking's past position - that all countries have a right to build atomic weapons - and the fact that China, a nuclear weapons state, is not a signatory to the Nuclear Nonproliferation Treaty add to the concern.
However, because the Chinese have moved away from prior positions, some arms control experts view the nuclear cooperation agreement as a positive move. ''We don't yet know enough about the agreement, but China's record was so bad, that anything you can get is a step of progress,'' comments a specialist at the Arms Control Association. ''Hopefully the agreement will provide a foundation for future cooperation and understandings.''
Says Joseph Nye, an expert at Harvard: ''The fact that China can be brought in a step closer to living with the rules of US legislation and with the international regimen is useful. If the Zhao toast was backed up by private assurances, by something more precise, this may be enough to be willing to go ahead and get China to play in the game.''
Others are more skeptical. ''I'm concerned that the Chinese assurances given were private and oral, so later we would have no way to hold them to it,'' says Leonard Spector of the Carnegie Endowment for International Peace. ''If there were a firm public declaration we could at least point to it and complain if there were a violation.''
''An oral statement by the Chinese does not have the same force as a statement in writing,'' says John Buell of the Nuclear Control Institute, a public-interest group. ''We got into trouble with India because of fuzzy language. Trade with China is not worth these kinds of problems.''
Another potentially controversial aspect of the proposed agreement are the so-called consent rights, including the provisions that China will not transfer US-supplied nuclear material to a third country, or enrich or reprocess it without prior US consent. Administration officials say these provisions are framed in ''diplomatic language'' which will enable China to stress US commitments while the United States emphasizes China's obligations.
''If these clauses are too ambiguous they may not stand up to the test,'' Dr. Nye says. ''There could be difficulties if the Chinese hold a different meaning. But there is an area where both can come to an understanding, where they don't rub the other party's nose in it.''