A provision tucked into the 1,724-page energy bill that Congress is poised to enact today would ease export restrictions on bomb-grade uranium, a lucrative victory for a Canadian medical manufacturer and its well-wired Washington lobbyists.

The Burr Amendment -- named for its sponsor, Sen. Richard Burr (R-N.C.) -- would reverse a 13-year-old U.S. policy banning exports of weapons-grade uranium unless the recipients agree to start converting their reactors to use less-dangerous uranium. The Senate rejected the measure last month after critics in both parties warned that it would accelerate the worldwide proliferation of nuclear materials, but a House-Senate conference committee agreed this week to include it in the final bill.

The amendment is just one of dozens of obscure special-interest provisions included in the energy bill, which the House passed yesterday and the Senate is expected to pass today. The amendment's supporters say it will ensure a steady supply of medical isotopes, which are used to diagnose and treat 14 million Americans every year, including patients afflicted with cancer, heart disease and epilepsy. But it will also be a boon to the world's leading producer of those isotopes, an Ottawa-based company called MDS Nordion, which would otherwise have to spend millions of dollars to retrofit its reactor for low-grade uranium.

Critics say the Burr Amendment will not only provide special perks for one foreign company but also encourage the proliferation that politicians in both parties have identified as a dire threat to national security in the post-Sept. 11 world.

In one House Energy and Commerce Committee meeting, Rep. Edward J. Markey (D-Mass.) demanded that lobbyists from the Alpine Group -- who have promoted Nordion's interests on behalf of a nuclear medicine trade group -- raise their hands and identify themselves.

"I've never done that before, but this is outrageous," Markey said. "To save one Canadian company some money, we're willing to blow a hole in our nonproliferation policies."

The Burr Amendment's supporters say there will still be plenty of safeguards to prevent terrorists from obtaining bomb-grade uranium. The amendment applies only to exports to Canada and four European allies, and its backers say they still expect isotope manufacturers to shift gradually toward less-dangerous uranium.

But Nordion uses U.S. uranium to manufacture isotopes for U.S. patients, and industry officials say that trying to force the company to shift could create massive shortages of a vital product.

"Our industry shares the concern about nonproliferation; we don't have our heads in the sand," said Roy Brown, director of federal affairs for the Council on Radionuclides and Radiopharmaceuticals. "When the technology is there, we'll all be willing to switch."

Opponents say the amendment would eliminate the financial incentives for foreign firms to switch. Since 1992, when then-Rep. Charles E. Schumer (D-N.Y.) persuaded Congress to adopt the export restrictions, Argentina and several other countries have begun retrofitting reactors to use uranium that cannot be used in atomic weapons.

By contrast, Nordion already has enough highly enriched uranium to make one or two Hiroshima-size bombs, and its factories do not have to meet the same security standards as Energy Department facilities. It initially agreed to convert to low-grade uranium, but its executives changed their minds and helped finance a fierce lobbying campaign to loosen the restrictions.

Burr first proposed his amendment in 2003, when he was a House member, and it was adopted by a conference committee before the energy bill stalled that year. This year, the House adopted his amendment again, and Burr tried to push it through the Senate, with support from Republican Sens. Christopher S. Bond (Mo.) and Larry E. Craig (Idaho), as well as Democratic Sen. Blanche Lincoln (Ark.). "To be able to provide the hope to those who suffer from these diseases is so critically important," Lincoln told colleagues.

Senate opposition was led by Schumer and Republican Jon Kyl (Ariz.), who warned that "were something bad to happen, each one of us would be responsible."

They cited the Energy Department's stated goal of ending the commercial use of weapons-grade uranium, and the department's public conclusion that there is no real shortage of medical isotopes. They also pointed out that uranium exported to any European Union country could be resold to another E.U. country without U.S. knowledge. They ultimately persuaded the Senate to reject the amendment in late June, 52 to 46.

The House and Senate still had to reconcile their energy bills, so Joe Barton (R-Tex.), chairman of the House Energy and Commerce Committee, and the panel's ranking Democrat, John D. Dingell (Mich.), proposed compromise language. But Pete V. Domenici (R-N.M.), chairman of the Senate Energy and Natural Resources Committee, said not to bother; Senate conferees would accept the amendment, even though the full Senate had rejected it.

"It really is amazing," said Edwin Lyman, a senior staff scientist for the Union of Concerned Scientists. "To get something as outrageous as this, that's skillful lobbying."

Since 2003, the Alpine Group's main energy lobbyists -- James D. Massie, Richard C. White and Rhod Shaw -- have contributed more than $25,000 to members of the energy committees, and nuclear medicine trade groups have donated tens of thousands more. They have also drummed up support from doctors; the computer signature on one letter to a senator, purportedly written by a radiologist, was actually White's.

Doug Heye, a spokesman for Burr, said the senator's support had nothing to do with lobbyists, and everything to do with the 40,000 medical procedures that use isotopes every day. There are plenty of isotopes to irradiate tumors and help doctors see through skin without surgery, but industry groups warn that unless Nordion and other manufacturers can continue to use bomb-grade uranium, patients could suffer.

"Certainly, there are concerns about proliferation," Heye said. "But we're also concerned about people with breast cancer."

Critics say that the danger of isotope shortages is highly remote but that the danger of terrorists seizing control of nuclear materials is quite real. During the presidential debates last year, President Bush and Sen. John F. Kerry (D-Mass.) both identified nuclear proliferation as America's most pressing foreign policy challenge.

"I don't recall them agreeing on much else," Markey said. "You'd think we could all agree on this."