TEHRAN, Nov. 20 - Iran's conservative Parliament approved the outline of a bill today that would bar United Nations inspectors from visiting its nuclear sites if the agency referred Iran's case to the Security Council for possible punitive measures.

The vote came before the International Atomic Energy Agency's board of governors was expected to review Iran's case on Thursday. The agency passed a resolution in September and called on Iran to suspend all its uranium enrichment-related activities before the meeting this month.

The Iranian measure needs to be approved by the Guardian Council before it becomes law. But the vote today, which was approved by 183 of the 197 lawmakers present at the session, suggests that Parliament backs the government's tougher stance over its nuclear program.

"By approving this bill, we are sending a message to the atomic agency," said Alaedin Boroujerdi, the head of Parliament's Commission for Foreign Policy and National Security, urging the agency not to act against Iran.

"Otherwise, we require the government to suspend all its voluntary measures," he said, according to the ISNA student news agency. Mr. Boroujerdi was referring to Iran's allowing inspection of its nuclear sites.

Iran defied an agreement with the three European countries, Britain, France and Germany in August and resumed activities at one of its nuclear sites near the city of Isfahan.

It further complicated diplomacy last week after it fed a new batch of uranium into the facility. The work includes converting mined uranium, known as yellowcake, into a gas, uranium tetra-fluoride, or UF4, a step before enrichment.

In a report on Friday, the head of the international nuclear agency, Mohamed ElBaradei, praised Iran's "transparency and indispensable" cooperation but also urged it to suspend its enrichment-related activities and to allow inspectors to visit a military site, Lavizan Shian, near Tehran.

Last year, the United States accused Iran of dismantling buildings at the Lavizan Shian site and removing topsoil from the area in an effort to hide nuclear-weapons related experiments. Iran contended that the razed construction was not related to military or nuclear work.

A Foreign Ministry spokesman, Hamid Reza Assefi, said today that Iran would only allow the inspectors to visit that site if they could provide "concrete proof" of weapons-related activity. "They cannot just say we want to talk to this or that person and keep dragging out the case," he said. "They should tell us their aims, and these aims should be towards closing the case."

He also brushed off references in the report to blueprints of detailed nuclear designs, saying they were "baseless," and "media speculation."

The report said Iran had turned over a document - which it never used - that said in 1987 it obtained blueprints of nuclear information from a network run by Abdul Qader Khan, the father of Pakistan's atomic program. Diplomats said the information could be used for making a nuclear bomb.