ON THE EVE of the Senate vote on whether to

exempt Pakistan from a restriction that prohibits aid to countries developing nuclear weapons, Sen. Alan Cranston has revealed some alarming news. He says, and the administration confirms, that there has been an increasing number of "anomalies," "irregularities" and unexplained breakdowns in the monitoring devices at Pakistan's Canadian-supplied reactor.

A few weeks ago, these led the director of the International Atomic Energy Agency, Sigmund Eklund, to take the--for him--extraordinary step of saying he could no longer vouch for the integrity of the IAEA's nuclear safeguards there. Mr. Eklund, you may remember, had such great faith in the IAEA's safeguards system that he brushed aside any suggestion that Iraq could misuse its reactor, only to be later flatly contradicted by an IAEA inspector and several independent nuclear experts. If Mr. Eklund is worried about what Pakistan is doing, that is a plain sign that there is plenty to be worried about.

Administration officials confirmed some months ago that Pakistan has been making swift progress on a clandestine reprocessing plant and appeared also to be readying a nuclear test site. The missing link had been where Pakistan would get the spent fuel to reprocess for its plutonium. The new information supplies that link.

Though the details are secret, Pakistan is reportedly adding nuclear fuel rods, made in its own unsafeguarded fabrication plant, to the safeguarded reactor and then, after the rods are irradiated in the reactor, removing them from the safeguarding system. There is enough "suspicious" activity to worry American intelligence agencies and the IAEA. Such fuel rods would constitute a plutonium stockpile, ready to be reprocessed whenever the reprocessing plant is ready.

In asking Congress to approve Pakistani aid, the administration never denied that Islamabad has nuclear intentions. But Undersecretary of State James Buckley testified he had "assurances" from its president that Pakistan did not intend to develop nuclear weapons, and he said he had made it clear in direct talks with Pakistani officials that the United States would not accept any distinction between a nuclear weapons test and a "peaceful nuclear explosion."

The administration strenuously opposes attaching any nuclear conditions to the aid package. It refused to state, at least publicly, that aid would be withdrawn in the event of a nuclear test. Its argument is that the rapid supply of F16s and other advanced weapons would relax Pakistan's security fears and bring enough leverage to dissuade Pakistan from its nuclear course. The burden is squarely on the administration's shoulders to use that leverage now.