Twice this week the Reagan administration warned Iran about the West's larger interest in Iran's strife with Iraq. President Reagan explicitly signaled Tehran about Iran's threats to close off the vital Strait of Hormuz, through which the Western world receives much of its vital oil supplies. Repeating warnings made by Secretary of State Shultz earlier this week, Mr. Reagan put the oil issue into a strategic context when he said he did not believe the ''free world would stand by and allow the Strait'' to be closed off.
The President, in his televised news conference Wednesday night, also carefully declined to spell out exactly what preventive measures might be taken by the United States and its allies. ''That,'' he said, was up to Iran ''to wonder about.''
Mr. Reagan correctly framed any US action as taking place in concert with other Western nations.
The strait links the Persian Gulf and the Indian Ocean. Through it comes roughly one-sixth of the oil used by the noncommunist world - mainly oil for Western Europe and Japan, and to a lesser extent the US. Any disruption in oil supplies through the strait could have far-reaching consequences for the major industrial nations. As a State Department analyst wryly notes, an oil disruption in the region has the ''potential to be quite nasty.''
While agreeing with the President that the strait must not be blocked, one cannot help regretting that firmer action had not been taken earlier by Washington to prevent the issue from flaring to the surface in the first place. What has triggered the current Iranian threat is the decision by the French government to deliver five Super Etendard jet aircraft to Iraq. Iraq, which has been stalemated in a war with Iran since 1980, could use the aircraft to fire Exocet missiles - the same type of missiles used by Argentina with such deadly results in the Falklands war.
Washington, to its credit, tried to persuade the French not to go ahead with the aircraft sale. France, however, went ahead despite the somewhat lukewarm US protests. Some reports - although unconfirmed - have it that the planes are now in Iraq.
Just how serious are the Iranian threats? That probably depends on whether Iraq decides to use the new aircraft to take out Iran's oil-loading terminal at Kharg Island, near the head of the Gulf. The facilities have so far survived attacks from conventional weapons.
Iran, it must be recalled, would be far more vulnerable than Iraq from any oil cutoff. Iran's oil exports of around 1.7 million barrels a day pass through the strait. Iran's imports - including food - arrive through the strait. By contrast, Iraq's oil exports reach the West by way of a pipeline through Turkey.
Any attempted cutoff by Iran would surely be met by determined allied action. The US already has a substantial naval presence in the area, including the aircraft carrier Ranger. The British also have a carrier and other ships in the region. France has sent minesweepers there in the past.
It would be militarily difficult for the Iranians to block the strait. There are two shipping channels, each running about two miles wide. But the Iranians need not totally blockade the waterway. Just sinking one tanker, or mining the strait, would send shipping insurance rates soaring and probably inhibit crews from venturing into the region.
Given the current world oil glut, any short-term cutoff from the Gulf would not have a major effect on supplies. Prices, however, could climb, as they did in 1979, when Iranian oil was cut off during the revolution. That jump in prices and long gas lines in the US - largely stemming from fears of supply disruptions - occurred even though other oil-producing nations more than made up for the lost Iranian exports. A more protracted shutoff, however, would obviously be serious indeed for Western nations now coming out of economic recession.