PARIS, AUG. 6 -- The French government, which is locked in a crisis with Tehran, today told oil companies operating in France to halt their growing purchases of Iranian crude petroleum.

The measure, announced by Industry Minister Alain Madelin, was aimed at preventing dependence on Iranian oil imports during a period of increased instability and risk in the Persian Gulf. It also responded to the belief in Prime Minister Jacques Chirac's government that buying large amounts of Iranian crude is inappropriate during a highly charged French-Iranian confrontation now in its sixth week, Madelin explained in a television interview.

France, which broke relations with Iran on July 17, dispatched a four-ship aircraft carrier battle group to the gulf area last week, doubling the number of French warships on station there. Chirac said the force, including advanced Super-Etendard fighters armed with Exocet missiles, would retaliate against Iran if French interests were attacked as threatened by the radical Islamic leadership in Tehran.

"It would be disorderly to see increases in Iranian {oil} imports in the current political situation," Madelin said.

Industry Ministry statistics showed Iran was the top crude oil supplier to France in June, supplying 5.03 million barrels out of a total of 35.6 million barrels imported overall in that month. In the first six months of the year, Iran was France's third-ranking supplier, behind Saudi Arabia and Britain.

By comparison, Iran was France's eighth-ranking supplier in 1986. This was the period in which Chirac's government was trying to normalize relations with Iran in hopes of improving chances for release of French hostages in Lebanon.

The sharp jump in purchases from Iran this year reflected prices set by Tehran at a level lower than those of competing oil sellers in the Organization of Petroleum Exporting Countries, Madelin said. The government in Tehran, which has been at war with Iraq for seven years, has been selling under fixed OPEC prices for some time in an effort to raise foreign exchange to finance its extensive military expeditures.

{According to figures supplied by the State Department, U.S. exports to Iran last year were relatively small -- totaling $34 million -- but imports, mostly oil, totaled $612 million. In Washington, State Department spokeswoman Anita Stockman said U.S. "export policy is under review, but no final decision has been made on whether or to what extent further trade restrictions on Iran might be made."

{According to the figures, the United States imported $460 million worth of crude oil from Iran, purchased on the spot market, in 1986. During the first five months of this year, the United States imported $418.5 million worth of Iranian oil.}

Madelin said he is counting on public opinion to force oil companies to adhere to the government's measure. This appeared to be one of the reasons for his declarations today, which confirmed rumors circulating here for the last week.

"It is not in the interest of any oil company before public opinion to go and import Iranian petroleum," Madelin said.

With oil contracts settled well in advance of delivery, Iranian petroleum shipments to France were expected to continue at least through the summer as long as the military situation in the gulf allows tanker traffic to flow.

In a parallel step, the government also criticized French service stations for what Secretary of State for Consumer Affairs Jean Artuis called "abusive" gasoline price rises. Responding to price rises on international petroleum markets, stations have increased prices at the pump by 8 to 12 cents a gallon in recent weeks.

The simultaneous announcements underlined the impact that gulf tension is having in France during a month usually devoted to sunbathing and tourism. Although Paris has refused to join the Reagan administration in providing military protection for gulf shipping, the standoff with Iran has dominated political life here.

French police have ringed the Iranian Embassy in Paris since June 30, demanding that an Iranian official holed up inside submit to questioning by a French judge investigating last fall's bombings that killed a dozen persons and injured more than 150. Similarly, Iranian Revolutionary Guards have surrounded the French Embassy in Tehran and neither country is allowing the other's diplomats to leave for home until the crisis is resolved.

In addition to the danger of military action in the gulf, the confrontation has clearly scuttled Chirac's attempt at normalization. If the embassy standoff continues, as some French officials fear, the crisis also could endanger Chirac's chances in presidential elections scheduled next spring. This has created an internal political dimension to the diplomatic struggle that Chirac's enemies here and in Iran apparently have sought to exploit.

The speaker of the Iranian parliament, Hojatoleslam Ali Akbar Hashemi Rafsanjani, repeated in a Tehran newspaper interview last week charges that Chirac's representatives had sought to delay release of French hostages in Lebanon before the March 1986 election that brought Chirac to power. Chirac immediately denied the charges, but several opposition Socialist figures have suggested there may be some truth to them.

This week the satirical newspaper Le Canard Enchaine, which also specializes in investigative reporting, published a letter it said establishes that Chirac is negotiating with Iraq to reconstruct the French-built nuclear reactor near Baghdad that was destroyed by Israeli bombs in June 1981.

Chirac's office confirmed that the letter was a genuine message from Chirac to President Saddam Hussein of Iraq. But a spokesman said the newspaper's interpretation of it was wrong. He insisted the prime minister was referring to debt rescheduling, not the nuclear reactor.

In its key passage, the letter referred to "the negotiation that you know about" and said Franco-Iraqi cooperation in that area is "capital for the sovereignty, independence and security of your country."