DUBAI, UNITED ARAB EMIRATES, NOV. 16 -- Iranian speedboats today attacked at least three foreign vessels in the strategic Strait of Hormuz, including a American-owned supertanker carrying Saudi Arabian crude oil, after a week of intensive Iraqi aerial attacks on Iranian shiping in the Persian Gulf.

The new Iranian attacks came as Iranian President Ali Khamenei reiterated threats of an impending ground offensive against Iraq by suggesting that students and at least one-fifth of the nation's civil service should enlist for service at the warfront.

Iran is rumored to have massed about 250,000 troops near the southern Iraqi port city of Basra in preparation for an offensive there.

Today's Iranian attacks, according to shipping officials here, were carried out by at least two Iranian speedboats that fired hand-held rocket-propelled grenades at their targets. No major damage or injuries were reported, according to shipping officials in contact with the ships.

The first Iranian attack came against the American-managed, Liberian-registered tanker Lucy as it sailed through the Strait of Hormuz at 3 a.m. local time.

Shortly before noon, two Iranian boats attacked the American-owned supertanker Esso Freeport, which is registered in the Bahamas, as it sought to leave the gulf with a cargo of Saudi Arabian crude oil.

The 250,000-ton ship, owned by the American oil company Exxon, was hit by four or five rocket-propelled grenades, according to shipping officials here, but the rockets did no damage except dent the ship's thick hull.

Two hours later, an attack on a Greek-owned tanker, the Filikon L, caused a small fire in the ship's engine room.

{A fourth, unidentified ship reported it was attacked about 15 minutes after the Greek tanker was hit and in the same area of the strait, The Associated Press reported.}

Although two of the ships hit by the Iranians today were either owned or managed by American firms, the United States was not expected to take the attacks as a direct challenge to its presence in the Persian Gulf.

U.S. Navy rules of engagement permit retaliation only if a U.S.-flagged vessel is attacked.

The Iranian attacks were not considered by diplomats here as a direct response to a near blitz of Iranian oil-transport ships in the last week by Iraqi planes firing French-made Exocet missiles.

Since Nov. 9, Iraq has claimed direct hits on 15 ships off the coast of Iran, most in the vicinity of the vital Iranian oil export terminal on Kharg Island, in the northern gulf. Independent sources have confirmed only three of the attacks Iraq has claimed.

Today's activity in the gulf came as the U.S. Navy escorted another convoy of reflagged Kuwaiti ships through the gulf without incident, the Pentagon announced. The Navy has built up an armada of at least 25 ships in the gulf since last July, when Washington agreed to provide military escorts for 11 reflagged Kuwaiti ships to defend them from attacks by Iran. Iran has singled out the oil-rich emirate of Kuwait for attacks because of its support for its neighbor, Iraq, in the seven-year-old gulf war.

The steady buildup of ground forces along the southern war front has given rise to speculation that Tehran plans a new push, possibly by the end of the year, toward Basra. During an offensive last January, Iranian forces penetrated to about six miles southeast of Basra. Iraq's second-largest city, it has a population of about 1 million.

President Khameini, in his speech broadcast by Tehran radio, repeated the call for a mobilization of forces to include students and civil servants. "It is useful for everyone to breathe the smell of the warfront," he said.