THE SENATE has now voted its assent to the nuclear cooperation agreement with China.

The United States is to sell reactor technology for the purpose of generating electricity, on the explicit condition that China does not divert it to military purposes and does not help other countries build nuclear weapons. The principle is clear; it's the enforcement that's in dispute.

The Reagan administration says that before it actually issues any export licenses it will negotiate "suitable procedures" for visits and exchanges of information with the Chinese. Sen. John Glenn points out that those terms imply something less than the inspections and materials accounting procedures that have been standard in the international effort to prevent the proliferation of nuclear weapons.

Because China already possesses nuclear weapons, the administration says, it falls into a special category. In the past the Chinese sometimes seemed ready actually to promote the spread of these weapons, but over the past several years there has been some change for the better in their attitudes. The administration contends that the nuclear agreement will reinforce their commitment to a policy of restraint.

But it is also true that, within the past two years, there have been disquieting reports of Chinese assistance to one country with large nuclear ambitions -- Pakistan -- and possibly to others. At the least, as Mr. Glenn points out, this agreement sets a precedent for relaxed surveillance that will make it more difficult to insist on international inspection in future agreements with other countries.

Last month Mr. Glenn introduced a bill that would require the administration to tighten some of the agreement's provisions. The administration strongly opposed it, on grounds that it would require renegotiation and jeopardize the whole agreement. The foreign relations committees of the two houses acknowledged that Mr. Glenn's criticisms were not trivial, but wanted to avoid a direct collision with the administration. Working together, the two committees wrote a compromise resolution that took note of Mr. Glenn's points and, in effect, told both the administration and the Chinese that Congress will keep an eye on the issues of compliance that he has raised.

That is the compromise resolution of approval that the Senate passed last week -- evidently the best that could be passed. Even among the Democrats there was not much inclination to take on the president directly in a foreign policy issue of such intricacy. We favored the tougher approach but believe the resolution is better than nothing. It at least imposes a degree of precision that, standing alone, the Chinese nuclear agreement would unfortunately lack.