WASHINGTON — On the five-year anniversary of the creation of President Bush’s flagship initiative to disrupt the global black market in apocalyptic weapons, one of the policy’s architects worries for its efficacy.

Mr. Bush’s national security adviser, Stephen Hadley, touted the Proliferation Security Initiative yesterday at a fifth anniversary “senior level meeting” at the Washington Hilton Hotel here. The initiative was created to keep chemical, germ, and nuclear weapon technology out of the hands of terrorist groups like Al Qaeda. It started as an alliance between nations like Australia, Britain, and Japan that would share intelligence, customs information, and naval resources to interdict rogue proliferators on the high seas and at border crossings.

But David Wurmser, who worked as an aide to Undersecretary of State John Bolton and helped develop the alliance, says he regrets that what was at first a small club of 7 nations has swelled its ranks to 90 countries, some of whom play both sides of the weapons of mass destruction black market.

Mr. Hadley took pains to explain that the initiative was no threat to international arms control regimes as he addressed representatives from the nations assembled, including China, Pakistan, and Russia. Some critics of the Proliferation Security Initiative have complained that it conducts treaty enforcement without the approval of the appropriate international treaty organization.

“PSI does not create a new enforcement mechanism,” Mr. Hadley said. “It uses existing enforcement capabilities effectively, cooperatively, and in a timely manner. Our nations must be able to act with the speed of commerce. If we are lucky, we must match the speed of a ship. If we are unlucky, we must match the speed of a jet plane.”

Mr. Wurmser said the multilateral arrangement he helped create was initially meant to be small. “This initiative was precisely an answer to the ossified, broad based proliferation structures that were failing us,” he said. “It was meant to be an association of like-minded nations genuinely worried and serious about counter-proliferation.”

Mr. Hadley pointed to successes. In February 2007, he said, four nations helped stop a shipment of ballistic missile technology headed for Syria. “A firm in one nation had manufactured the equipment. A firm in another nation was the intermediary that sold it to Syria. The shipping company was flagged in a third nation. And customs officials at the port of a fourth nation were alerted to offload and inspect the equipment — and send it back to the country of origin,” he said.

Mr. Wurmser would not discuss the details of the transaction, but did note that the technology was ultimately shipped back to the country of origin.

“Compare the BBC China interdiction to the incident that Hadley mentioned,” Mr. Wurmser said, referring to the October 2003 interdiction of centrifuge components headed for Libya that gave American negotiators the leverage to pressure Muammar Gadhafi into admitting he had a nuclear program.

“Who actually had control of the proliferating material in the BBC China at the end of the incident, and who actually held control of the material at the end of this event that Hadley describes?” Mr. Wurmser asked. “As Hadley says, it was the proliferator, whoever it is, who held on to the material. In the BBC China case, the Germans held onto the centrifuge parts.”

Mr. Hadley said he was particularly concerned about terrorist groups obtaining weapons of mass destruction. He raised the specter of Iran — which enriches uranium in defiance of three U.N. Security Council resolutions — funneling chemicals, germs, or radioactive material to terrorists. “The position of the United States and many nations in this room is clear: We will not betray future generations by allowing Iran to have a nuclear weapon,” he said.