The Defense Department, citing the threat of terrorist activities and underwater mines, has authorized "imminent danger" pay bonuses for about 10,000 military personnel serving in the Persian Gulf region, Pentagon officials announced yesterday.

Military personnel on duty in the Persian Gulf, the Strait of Hormuz, a small area of the Gulf of Oman, Kuwait and Bahrain, as well as airspaces over those regions, will qualify for the $110-a-month bonus, according to David J. Armor, acting assistant secretary of defense for personnel.

The bonus will cost the government $1.1 million a month, Armor said.

"Our review of the situation in the gulf area indicates that the special pay is warranted on the basis of terrorist actions and other conditions," Armor wrote in his order authorizing the pay. The bonus took effect Tuesday.

Armor said the area will remain designated for the special pay "until we make an assessment that it's no longer warranted."

Some members of Congress, who believe the War Powers Resolution should be invoked to permit Congress to decide whether U.S. warships should continue to escort reflagged Kuwaiti tankers through the region, said the Pentagon decision strengthens their case.

Senate Foreign Relations Committee Chairman Claiborne Pell (D-R.I.) described the decision as "just one more reason why the war powers act should apply" to the Persian Gulf operations.

Administration officials contend that different legal standards govern the War Powers Resolution and the provisions for imminent danger pay, formerly called "combat pay."

"The broader language and history of this authority makes it clear it is available in situations where War Powers Resolution is not applicable," said national security adviser Frank C. Carlucci. "The special authority applies where there is a threat of physical harm or imminent danger. The war powers apply only when imminent involvement in hostilities is clearly indicated."

But Pentagon officials said some administration officials were reluctant to authorize imminent danger pay.

"There were obvious concerns about the War Powers {Resolution}," said one Defense Department official familiar with the decision-making process.

Only three weeks ago Armor told a House Armed Services subcommittee, "The threat to U.S. warships in the gulf is lower than that posed by terrorism ashore in many Middle East countries. A general threat of terrorism has never been the basis for declaring imminent danger; rather, we have always required specific identifiable threats of physical harm or imminent danger to military personnel."

Armor said at a news briefing yesterday that since his statements to the House panel, additional mines have been discovered in the Gulf of Oman near the entrance to the Strait of Hormuz. Armor said the decision also was based on some threats that he declined to identify because they are "classified."

"It's been a very dynamic situation," Armor said. "Many changes and new events happen each week."

{A branch of the pro-Iranian Hezbollah (Party of God) yesterday threatened to turn U.S. and Saudi Arabian bases into graveyards if the United States does not withdraw its warships from the gulf region by next Tuesday, Reuter reported.

{In a handwritten statement delivered to international news agencies in Moslem West Beirut, a group calling itself "The Sons of Hezbollah -- Hijaz" accused "navies of the big forces" of threatening Iran's Islamic revolution and gave the United States a week to pull out of the region, Reuter said.}

Armor said the Defense Department decision came in response to a request for the special pay from Gen. George Crist, chief of the Central Command, which has jurisdiction over U.S. forces in the Middle East. He said several other areas have been designated as zones for imminent danger pay in past years -- including Peru, Colombia, Sudan, El Salvador, Iran, as well as Libya and Grenada during U.S. military operations there.

The sailors and officers aboard the USS Stark were paid a one-month bonus retroactively after an Iraqi pilot fired two missiles at the ship, killing 37 sailors on May 17.

The 10,000 personnel who will qualify for the bonus pay represent about half of the U.S. forces now on duty in the Middle East region. Armor said sailors and officers assigned to the aircraft carrier group and other vessels in the Northern Arabian Sea would not qualify for the pay.

Air crews on planes that are based on the carrier and fly missions over the designated Persian Gulf region would be qualified to receive the extra pay, he said.

Pentagon officials said yesterday that the amphibious cargo ship USS St. Louis joined the fleet inside the Persian Gulf temporarily. Pentagon sources said the ship, which arrived Tuesday, was carrying small mine-sweeping vessels as well as speed boats operated by the Navy's SEAL (Sea, Air and Land) special forces antiterrorism teams.

The ship will leave the gulf after it unloads, according to Pentagon sources.

While most of the personnel who will receive the bonus pay are based on ships in the Persian Gulf, other Navy, Air Force and Army personnel in the area will also receive the bonuses.

"I think the significance of this goes far beyond the imminent danger pay," said U.S. Rep. Barbara Boxer (D-Calif.), one of 114 members of Congress and the Senate who have filed a lawsuit asking a federal judge to order President Reagan to invoke the War Powers Resolution. "If there is concern by the Pentagon that there is imminent danger in the gulf, that is exactly the requirement for invoking the War Powers Resolution."

Since July, U.S. forces have escorted through the gulf five convoys of Kuwaiti tankers now flying the U.S. flag. The War Powers Resolution would require congressional authorization for continued operations after a period of 60 to 90 days.

One White House official said yesterday that "we fully expect added pressure" to invoke the War Powers Resolution when Congress returns in September. Carlucci, speaking to reporters in Los Angeles, said yesterday that the question of whether the resolution applies to the gulf situation is "under constant review."

White House chief of staff Howard H. Baker Jr. originally proposed using the War Powers Resolution when the initial decision was made to reflag the Kuwaiti tankers and provide U.S. warship escorts. But the president accepted arguments of Pentagon and State Department attorneys that such action would be unnecessary.

Pell said that Congress may find it increasingly difficult to legislate military constraints as U.S. involvement in the region intensifies. "It's hard to invoke the War Powers when you're already involved up to your armpits."Staff writers Helen Dewar and Lou Cannon contributed to this report.