LONDON, SEPT. 23 -- Britain ordered Iran to close its controversial weapons procurement office here today and gave its staff of about 30 Iranian military officials two weeks to leave the country.

The closure of the Iranian office, which government sources here have said does the paper work on an estimated 70 percent of Tehran's worldwide weapons purchases, was the first concrete western move to curtail the flow of arms since the events of Monday, when U.S. forces in the Persian Gulf attacked an Iranian boat said to be laying mines, and a British-flagged tanker was hit by Iranian rockets.

One Filipino crew member was killed and 33 were injured in the rocket attack on the tanker Gentle Breeze, registered in the British colony of Hong Kong.

In a speech to the U.N. General Assembly today, Foreign Secretary Geoffrey Howe said that the "cynical" attack on the Gentle Breeze had been the "last straw." Howe called on "the United Nations as a whole to learn the same lesson" as Britain "from what Iran has said and done this week," and move toward an arms embargo against Tehran.

Iranian President Ali Khameini, speaking to reporters in New York, denied that Iran had attacked the Gentle Breeze, and dismissed the order to close the London procurement office as "not at all of substantial importance."

Sources here said that although the operations conducted at the office could be carried out elsewhere, its removal would complicate Iran's arms buying arrangements. Officially known as Iran's Logistics Support Center, the office is near Parliament at Westminster. The six-story building, purchased by the shah of Iran in the 1970s, houses hundreds of workers employed by the official Iranian trade center, oil company and other state organizations.

London has provided a convenient base from which to solicit bids for filling Iran's weapons needs. Iranian and other banks located in London have been used to transfer funds to a network of primarily European suppliers, many of whom are believed by law enforcement officers to have acted in violation of various nations' laws against exports to Iran.

European purchases are said by sources here to have become more difficult in recent months as western governments have cracked down on illegal sales. But a report last week from United Press International, based on documents obtained from the office, said that recent deals arranged in London include the purchase of 80 pilotless, remote-controlled aircraft from Taiwan in February, and a $500 million order on June 21 for the purchase of Chinese-built Scud B missiles from North Korea.

The British government has been under pressure from U.S. officials and from its political opposition to close the office. But officials from Prime Minister Margaret Thatcher and Howe on down repeatedly have insisted that the Iranians were breaking no law as long as they did not violate Britain's own restrictions on sales to Iran.

Those restrictions barred the sale of any "lethal" British goods deemed capable of expanding or exacerbating the Iran-Iraq war. Sales approved as legal in recent years have included engines and spare parts for British-made Chieftain tanks, as well as a radar system to control air traffic and up to 3,000 Land Rovers.

Parliamentary opposition became more intense last June when a diplomatic row between London and Tehran resulted in each cutting back the other's diplomatic staff to one person.

But on July 1, Howe said the dispute with Tehran was "a consular and diplomatic matter and it would be wrong, for the sake of British industry and jobs, to disregard the fact that . . . we still have a substantial export trade with Iran, which is conducted entirely within the law."

Whether the nonmilitary part of that trade will continue, British officials said today, is up to the Tehran government. Britain last year maintained a total trade surplus of about $500 million with Iran.

"We have no wish to see the others leave or to stop operating," a British spokesman said of the remaining Iranian operations here.

Officials here acknowledged that although several of the Iranian arms deals are under investigation, Iran still has not been found in violation of British law. The decision to close the office anyway, one official said, was "obviously political."