THESE ARE nervous times in the Persian Gulf, but the judgment of one careful and informed community, the shippers and insurers, is worth noting. Traffic is near normal. Yesterday an American-escorted convoy of three tankers arrived safely in Kuwait. Mines are about, but mine-sweeping duties are being taken up, separately, by the United States, Britain and France. Gulf Arabs are apparently providing somewhat more support than they choose to acknowledge.

It is headline news that American warplanes fired two missiles at an Iranian aircraft ''perceived'' to be threatening a U.S. patrol plane on escort duty. It seems the missiles hit no Iranian aircraft, but one can hope they had an impact on the Iranian political consciousness. The jitters about American policy widely expressed in the United States may have made some Iranians doubt that the United States was serious about its escort mission. It is conceivable that Iranians fail to see clearly the difference between the powerful popular dissent to the Reagan policy in Central America and the anxious but unmistakable consent to the Reagan policy in the Gulf. Demonstrating a readiness to defend ships and planes doing escort duty could be a useful antidote to any Iranian misperception on this score.

A cease-fire of sorts had been in effect at sea as a result of the unanimous U.N. Security Council resolution voted last month. This partial pause had given definite advantage to Iran, which is proportionately far more dependent on sea traffic than Iraq and which, meanwhile, mocked the cease-fire appeal and continued to press the ground war it long ago carried to Iraqi soil. Now Iraq has resumed air attacks against Iranian oil and economic targets on land. An Iranian response is awaited.

What might it be? Rep. Les Aspin, chairman of the House Armed Services Committee, has been warning that Iran's military strengths in confronting the United States lie in the ''no-fingerprints,'' low-tech domain of terrorism, ''invisibly'' laid mines and the like. A further example lies in the recent staged riots of Iranian Moslem pilgrims in Mecca -- riots that the Saudis, belying their reputation of timidity, effectively contained. The low-tech area, however, does not belong to Iran alone. That a ship carrying Iranian oil took a hit over the weekend may remind Tehran, all of whose cargoes come in and out by sea, that mines are a threat to every country's shipping.

Iran appears to be in an unusually contrary and defiant phase. Still, it is right that the United States tries to go about the military business as sensibly as it can and at the same time, with the Soviet Union and others, holds open the vital alternative of ending the Iran-Iraq war.