The Reagan administration vowed yesterday to continue naval escort of Kuwaiti supertankers through the Persian Gulf despite a mining incident that damaged the Bridgeton, but four senators predicted further attacks and later introduced legislation to stop the escorts.

White House spokesman Marlin Fitzwater, who earlier in the day said that retaliation against Iran for the attack is "not a consideration at this time," described the warship escorts as part of a "long-term U.S. commitment" that would be continued.

President Reagan reaffirmed U.S. commitment to the operation at a meeting of a National Security Planning Group (NSPG) yesterday morning, officials said. A senior aide said there is "no proclivity for retaliation" but added that the president wanted to know whether the mine was Iranian in origin and the attack deliberate before completely ruling out counteraction.

Fitzwater said that Reagan was awakened by National Security Adviser Frank C. Carlucci at 2 a.m. and informed of the incident, which occurred three hours earlier. The president was given another update at 9:30 a.m. before the NSPG meeting, the spokesman said.

The mine, which tore a hole in the port side of the 401,382-ton Bridgeton, about 120 miles southeast of Kuwait, touched off renewed opposition on Capitol Hill to the Reagan administration policy of reflagging 11 Kuwaiti oil tankers and sending them through the gulf with U.S. escorts.

Sen. Dale Bumpers (D-Ark.), joining with three other senators to sponsor legislation that would cut off the escorts in six months unless Congress specifically extends them, said at a news conference that the reflagging policy "literally makes the American flag a shooting gallery -- an inviting one to Iran."

Senate Majority Leader Robert C. Byrd (D-W.Va.) said the Bridgeton incident was an example of "one of the perils of the administration's hastily thought out and . . . still ill-conceived plan."

Later, on the Senate floor, Sen. John W. Warner (R-Va.), ranking Republican on the Senate Armed Services Committee, took issue with Bumpers. Warner said he had shared other senators' initial misgivings about the reflagging but urged support for it now that it has begun. This is a time for "cool heads and serious minds . . . free of rhetoric," he added.

Carlucci reiterated the U.S. commitment to the escorts and declined to put a time limit on how long they will continue. He said the U.S. government would make "a unilateral decision" on how long escorts are necessary, depending on evaluation of the military threat to the tankers.

Administration officials tried to play down the significance of the incident. They said that the mine struck by the 1,200-foot Bridgeton was far away from any area where mines had previously been detected. Fitzwater praised the escort operation, calling it "a success except for the mining incident."

Officials said Reagan was told that the mine probably was laid from Iran's Farsi Island, which has been a launching point for attacks on shipping in the seven-year-old Iran-Iraq war. Cmdr. Daniel J. Murphy Jr., skipper of the destroyer USS Kidd, one of three U.S. warships escorting the Bridgeton and the Gas Prince, said it is his "personal belief" that the mine was laid the night before from Farsi Island, although he added he had "no proof" of this.

Despite the strongly negative reaction of some congressmen, there was little indication that the incident by itself would prompt Congress, which is on record against the reflagging, to take more than symbolic action. But some congressional sources suggested that the sentiment could change quickly if American lives are lost in a future incident.

"There's certainly a difference between a mine and a deliberate attack," said Sen. Alan Cranston (D-Calif.). "I don't think it will have an impact on the sentiment in Congress for reflagging. Congress has already demonstrated its feelings. It doesn't change anything, but it does demonstrate the danger of our current policy in the gulf."

At least four other tankers have struck mines in the northern gulf since mid-May, including the Soviet tanker Marshal Chuikov, one of three Moscow has leased to Kuwait.

The Chuikov, the first to strike a mine on May 17, was being escorted at the time by a Soviet frigate, which took no retaliatory action against Iran. But the Soviets issued a stern warning and sent a high official to Tehran for talks that presumably included the Iranian mine threat to Soviet shipping.

U.S. officials had thought the mine threat was confined to the main channel leading into Kuwait's main oil terminal at Ahmadi and had been largely resolved. The Bridgeton was hit about 40 miles farther south.

Pentagon spokesman Robert B. Sims said the United States believed the threat had been "minimized" because a dozen mines had been found in the main channel and detonated.

The U.S. naval force assembled to escort the reflagged Kuwaiti tankers does not include any mine sweepers. By contrast, the Soviets have three mine sweepers in the gulf to protect Soviet-flagged ships and only one warship.

When the first Iranian-laid mines were discovered in late June, the Pentagon first considered sending five Navy MH53 mine-sweeping helicopters with 200 support personnel to Kuwait to clear them.

Instead, U.S. defense officials decided to send an 18-man team of mine warfare specialists who operated from small boats. They discovered about 10 mines, marked them with flags and later detonated them.

The mines, attached to the bottom of the sea, were discovered to be of North Korean manufacture and were considered rather old and unsophisticated. But U.S. officials concluded that they had been deliberately placed there by Iran.

Bumpers was joined in his legislative proposal to cut off escorts by Sen. Mark O. Hatfield (R-Ore.), Sen. Brock Adams (D-Wash.) and Sen. Frank H. Murkowski (R-Alaska.) Adams said the White House decision to protect the Kuwaiti tankers was the gravest foreign policy decision made by the United States since the first Marines were sent to Vietnam.

The bill would allow operations to go ahead unimpeded for six months after enactment. But the operation could then be extended only if the president, within 40 days of the end of this period, certifies to Congress that continued reflagging is in the national interest and a resolution approving it is passed by Congress.Staff writers David Ottaway, Helen Dewar and Molly Moore contributed to this report.