A SOUND PLAN for dealing with nuclear wastes has eluded this country for the third of a century since controlled nuclear fission was first discovered. So perhaps it is a fantasy to expect that Congress might actually get a program on the books in the last frenzied days of this session. Yet the possibility is there, and for the good of the country and the health of its nuclear industry, the moment should be seized.

The problem in this Congress has not been a lack of ideas about what to do with the wastes. It has been a surfeit of conflicting plans. This week, after months of struggling, the House finally reached agreement on a single approach. The bill it passed is admittedly only a partial solution: it includes a plan for long-term disposal of nuclear wastes but does not grapple with the more immediate need for facilities to store spent nuclear fuel. But it does finally establish a firm timetable for choosing a site for the nation's first nuclear waste repository and a sound mechanism for ensuring that the choice will prove to be technically and politically feasible.

The bill also provides a reasonable solution to the vexing problem of whether a state should have the right to veto the siting of a waste facility within its borders. This is no theoretical matter: 16 states have already passed laws forbidding waste repositories. The bill allows a state to say no to a proposed facility, but that negative vote must be supported at least by either the Senate or the House in order to block the facility.

Led by Sens. Jackson, Johnston and McClure, the Senate is trying to agree on a minimal package of amendments that would make the House bill acceptable on both sides of the Capitol. There is every reason to think that such an agreement can be reached -- at least between those most involved with this issue. The chief fear is that the compromise will be torpedoed by one of the many senators with nothing left to lose under the Senate rule that allows a single member to block legislation.

The House bill and its probable Senate amendments will fully satisfy no one. Yet it represents real progress on the nuclear waste problem -- progress that is decades overdue. The House bill passed with the support of both the nuclear industry and the the support of both the nuclear industry and the major environmental groups, testimony that those who know the most about nuclear waste recognize that this bill -- like the Alaska lands and Superfund cmpromises that have preceded it -- is preferable to more years of controversy and delay. For the first time, a nuclear waste disposal plan is within Congress' grasp. It will be terrible if it is allowed to slip away.