U.S. officials are pressing the Belgian government to reject a $1 billion nuclear cooperation agreement with Libya that U.S. officials fear could help Libya learn to build nuclear weapons.

Belgian officials have said the Libyan offer, which is under consideration by the Belgian cabinet, calls for building nuclear energy facilities in Libya without providing militarily useful technology. U.S. and Belgian officials said the Belgian economy is sufficiently weak for Brussels to be tempted by the offer to the government-controlled firm of Belgonucleaire.

U.S. officials said they are skeptical of the motives of oil-rich Libya and its leader, Col. Muammar Qaddafi, in seeking nuclear technology and would prefer that the deal be rejected outright, without compromise. Washington considers Qaddafi unpredictable, lawless and a major backer of terrorist activities outside his nation.

"First it's a civilian reactor, then it's a little reprocessing, and next thing it's a bomb," a senior administration official said.

"Belgonucleaire is persuaded that they could deliver nuclear plans to Libya without danger that they will be used for military purposes," a Belgian official said. "The problem, as you know, is that the American government is not really pleased with the project."

The official added, "The government knows very well that Qaddafi is not an angel."

The controversy is the most dramatic in a series of disputes between Washington and Brussels centering on Belgium's desire to export high-technology products to communist nations. Defense Secretary Caspar W. Weinberger and other Pentagon officials are reported to be furious about what they consider to be a Belgian double cross in another technology-transfer case.

That case centers on a small Belgian company called Pegard that wanted to export a sophisticated machining tool to the Soviet Union, where western intelligence officials believe that it would be used to make SS20 and SS21 missiles. After a tense standoff last summer -- with the crated $1.6 million machine sitting on an Antwerp dock, a Soviet freighter just offshore and KGB agents watching around the clock -- U.S. officials believed that they had resolved the case by agreeing to pay Belgium $680,000 not to export the machine.

Two weeks later, however, the Belgian cabinet licensed Pegard to sell the Soviet Union five other machines, which Belgian officials said are less sophisticated. U.S. officials, not convinced that the machines are harmless, felt as if they had been "slapped in the face," one Pentagon official said. The United States has not sent the $680,000 check.

Weinberger may discuss the Pegard case with Belgian Defense Minister Freddy Vreven at a NATO conference in Italy this week, a senior Pentagon official said. Even if the subject is not on the agenda, the official said, "they can hardly keep it from coming up."

Despite U.S. frustrations about both issues -- "It's nearly a habit for them not to be pleased," a Belgian official said -- U.S. officials do not want to strain the alliance or the Belgian government too much. Unlike the Netherlands, Belgium is loyally on track with its pledge to deploy U.S. nuclear cruise missiles next year.

"On that one, the Belgian government is the good boy of the class," a Belgian official said.

The Libyan government has been shopping around Europe for a company or nation willing to build nuclear energy facilities in Libya, U.S. officials said. The Belgian deal is the closest they have come so far, they said.

Albert Carnesale, a nuclear proliferation expert at Harvard University, said stories have circulated for years that Qaddafi was seeking to buy nuclear weapons or was working with Pakistan in their development. He said that he has never seen evidence to support either story and that Libya is not close to being able to build such weapons.

Belgian officials have said they would build civilian reactors in Libya and supply technicians to monitor them during a "transition period." They have pointed out that Libya has signed international treaties pledging not to develop nuclear weapons, so that facilities would be under international observation.

They also have said the proposed $1 billion deal does not include any reprocessing technology, but U.S. officials said they are unsure about that point. A nuclear reactor cannot produce a nuclear weapon, but reprocessing spent fuel from that reactor is an important step in learning to build a nuclear bomb.

Carnesale said that in recent years the line between the technologies for peaceful uses of nuclear energy and militarily useful ones has become increasingly blurred. He said that even learning to handle radioactive materials could help a nation trying to build a bomb.

A Belgian official said that, with unemployment and budget deficits both running high, the $1 billion deal will be hard to turn down. Officials of Belgonucleaire, which is partly government-owned, have been lobbying the cabinet intensively to say yes.

"We have the technology to build nuclear bombs, because every industrial nation has that capacity," the official said. "But we would not provide that technology to Libya."

The Pegard case is more complex and, if anything, more irritating to U.S. officials. Pegard is 75 percent owned by a German firm, Voith, which several years ago tried unsuccessfully to export exactly the same computerized tool-and-die lathe to the Soviet Union.

This time, Pegard applied for a license indicating that the machine would be used for the manufacture of boilers. Belgian officials became suspicious when several Soviet engineers, denied visas to enter Belgium, showed up on tourist visas and began helping out at the Pegard plant near Liege.

A Belgian customs official noticed the machine on the dock just before the Soviet freighter would have picked it up. Pegard is in financial trouble and in danger of closing, so U.S. officials eventually agreed to pay the Belgian army the $680,000 to help it buy the machine, which was more sophisticated than the army needed.

But on Sept. 15, the cabinet let it be known that five additional machines could be shipped. According to a Belgian official, economics minister Marc Eyskens acknowledged that the five could be used to produce precision weapons if upgraded with German-built computers, but he argued that that was a problem for West Germany, not Belgium.

U.S. officials are still studying the deal. Eyskens met with Weinberger and Commerce Secretary Malcolm Baldrige 10 days ago but failed to resolve the issue.