Pakistan, working through its embassy in France and intermediaries in Canada and Switzerland, tried at least three times this year to buy American-made, high-temperature furnaces that can be used in manufacturing nuclear weapons, according to documents furnished yesterday to administration officials and congressional investigators.

The furnaces Pakistan sought, made by the Consarc Corp. of Rancocas, N.J., are more advanced technically than similar pieces of equipment whose shipment to Iraq was stopped at the docks in August because of their potential use in making nuclear weapons, officials familiar with the documents said.

Further, the documents show that British authorities were informed in August that Pakistan was trying to buy similar furnaces from German and British manufacturers as well as another American company.

The documents, which were obtained by The Washington Post, surfaced as Pakistan's nuclear weapons program is coming under increasing attack in Congress from lawmakers who are are pressuring the administration to cut aid to the South Asian nation because of its nuclear program. {Details, Page A14.}

Partially reacting to this pressure, President Bush last week withheld military aid and future foreign aid until he can gain greater assurances from Islamabad that Pakistan does not have nuclear weapons and is not trying to build them.

Pakistan has steadfastly denied for years that it possesses nuclear weapons or maintains a nuclear weapons program, but administration officials and lawmakers are now greeting these assurances with greater disbelief. Nuclear nonproliferation experts believe Pakistan has pursued a nuclear weapons program ever since its neighbor and longtime foe India exploded a nuclear device in 1974.

In Islamabad on Monday, Prime Minister Ghulam Mustafa Jatoi said Pakistan had provided an "assurance" to President Bush, similar to those given in the past, that Pakistan's nuclear program is peaceful, Reuters reported.

No one was available at the Pakistan Embassy here to comment on Pakistan's efforts to buy the furnaces.

The paper trail of documents shows that, starting in February, Pakistan approached Consarc Corp. with requests to buy arc melting furnaces that cost about $3 million each. The requests came to the company's New Jersey headquarters as well as to one of its salesmen in Canada and to its British subsidiary.

In all cases, the orders were refused because of U.S. and British restrictions on the sale to Pakistan of equipment that could be used in a nuclear weapons program.

U.S. authorities said the furnaces would allow Pakistan to create the kind of system needed to produce both nuclear materials pure enough to make a bomb and metals that could be used to make missiles to deliver nuclear weapons.

They also cited the "circuitous approach" used by Pakistan -- seeking the same item through different channels and from different sources -- as evidence that the furnaces would be used in a clandestine nuclear weapons program.

"Judging from the routes they are coming in from, it is clear that Pakistan is trying to hide their real use," said one government specialist.

In turning down the bid of the Swiss company, Fernhandels A.G. Basel, Consarc salesman Manfred Dickersbach wrote that "many other agencies and firms" have tried to buy the furnaces on behalf of Pakistan, according to the documents. Dickersbach also noted that the specifications supplied by the Swiss company do not match the end result called for. Finally, Dickersbach said flatly that the material to be processed in the furnace "appears to be zirconium" -- which is used to sheath reactor fuel.

"It sounds like part of a fuel fabricating operation," said Leonard A. Spector, a specialist in nuclear nonproliferation issues at the Carnegie Endowment for International Peace in Washington.

The requests to sell the furnaces came from a variety of sources, according to the documents. The first was sent to Consarc's British subsidiary on Feb. 2 from the Pakistan Embassy in France. In March, Sen. John Glenn (D-Ohio) charged that the embassy helped to arrange for the illicit export from West Germany of technology and equipment associated with the manufacture of hydrogen bombs.

In April, the documents show, the company informed S. Muhtar Ahmed in Pakistan's Embassy in Paris that it could not get an export license to supply the furnaces.

In mid-February, meanwhile, Al Ferrari, a Consarc salesman in Canada, was asked by a Toronto consulting firm with Pakistani connections, Central Diagnostic Inc., about supplying furnaces to make high-quality steel suitable for surgical equipment, according to the documents.

Malik Khalid, an official of Central Diagnostics, denied that his company had anything to do with Pakistan's nuclear program. He said in a telephone interview yesterday that his company decided not to go ahead with the order because Consarc's furnaces are "too expensive" for Pakistan's small surgical equipment industry.

The search continued in April, when Pakistan's Directorate of Technical Procurement in Islamabad asked Consarc's British branch about buying six furnaces.

And four days after the Pakistan Embassy in Paris was turned down in its try to buy the furnace, the Swiss firm, Fernhandels, made its first approach to Consarc. According to the documents, Fernhandels sent the identical specifications supplied by the Pakistan Embassy in Paris to Consarc's New Jersey headquarters and followed up three weeks later with a letter seeking to buy other types of furnaces. Fernhandels attached the same specifications to that second request that the Directorate of Technical Procurement used in trying to buy the furnaces from Consarc's British branch.