WASHINGTON--President Reagan, calling Americans "a compassionate people," said yesterday the U.S. government will compensate the families of those who perished in an Iranian airliner shot down by a U.S. Navy cruiser.

Without admitting legal liability for the loss of 290 lives when Iran Air Flight 655 was downed July 3, Reagan said the payments should be made on behalf of "the innocent people who were the victims."

There was no immediate indication how much money would be involved, and a State Department official said "we have a lot of facts to investigate" before any payments are made.

In Congress, whose approval apparently would be required, House Speaker Jim Wright (D-Texas) said lawmakers are likely to be sympathetic to Reagan's request, but some members called the request premature because of still-unanswered questions about the incident. Some said compensation should be paid only after Americans being held hostage in Lebanon are freed.

In its announcement, the White House said there would be no lowering of the U.S. military profile in the Persian Gulf. And Reagan stressed that "there's certainly going to be no compensation" for the Iranian government.

On the eve of a scheduled United NationsSecurity Council debate on the incident, theadministration said ultimate responsibility restswith "those who refuse to end" the Iran-Iraq war,especially Iran "which has refused for almost ayear to accept and implement Security CouncilResolution 598, while it continues unprovokedattacks on innocent neutral shipping and crews inthe international waters of the gulf."

"We will not countenance any impression thatthis is a payment to the government or anadmission of liability or is in response to anyother external pressure or external internationalpolitical condition between our two countries,"White House spokesman Marlin Fitzwater said.

At the Iranian mission to the U.N. in New York,spokesman Amir Zamani declined comment on theWhite House statement. He noted that IranianForeign Minister Ali-Akbar Velayati will addressthe Security Council meeting this afternoon and isexpected to comment on compensation.

Amid conflicting reports about whether Iranrecovered the flight recorder from the downed A300Airbus, the White House said anew that Capt. WillC. Rogers III, commander of the USS Vincennes,took "justifiable defensive actions" to protecthimself against feared attack by an Iranian F-14warplane.

Fitzwater also said he wasn't sure whether theadministration would have to ask Congress toappropriate the compensation payments but that itwould not hesitate to do so.

A State Department official who briefedreporters on condition of anonymity said it wasnot yet clear whether a flat amount will be paidfor each victim or whether the age, number ofdependents and earnings of the victims will betaken into account in assessing compensation.

"We have a huge job ahead of us," he said. "Wehave a lot of facts to investigate."

Reagan, asked whether giving compensation mightsend a bad signal, said, "I don't ever findcompassion a bad precedent."

On Capitol Hill, Wright said, "If the presidentis satisfied [that payments are warranted], Iwould imagine the Congress would be satisfied."

But House Democratic Whip Tony Coelho ofCalifornia, the party's chief vote-counter, saidhe believed the request would "have some problems"and said he was personally opposed to it.

Sen. John McCain (R-Ariz.), a former prisonerof war in Vietnam, said that as long as Americansremain hostage in Lebanon by pro-Iranian elements,"there will be resentment to any payment, to anyIranian, under any circumstances."

Fitzwater made clear that the money would bechanneled through some third-party organization orintermediary, such as the Red Crescent, an arm ofthe Red Cross, and not the Iranian government.

He acknowledged that the U.S. government hadnot yet addressed the question of how, and withwhom, to verify the identities of the dead orsurvivors who will likely make claims forcompensation.

All but 38 of the Iran Air passengers were fromIran. The others were from India, Italy, Pakistan,Turkey, Yugoslavia and the United Arab Emirates.

During a picture-taking session with SalvadoranPresident Jose Napoleon Duarte, who isrecuperating from cancer surgery here, Reagan toldreporters, "I, from the first, have said we're acompassionate people, and I think that we all havecompassion for the families of those unfortunatepeople who were on that plane."

The president said he understood a recentpublic opinion poll showing a majority ofAmericans opposed the granting of compensation,but said, "I think that they have tied that to ourfeelings about the government and what it did withregard to our people in the embassy there [inTehran in 1979], when the Ayatollah [RuhollahKhomeini] came in [to power]."

The administration left several questionsunanswered. Fitzwater said he had no idea of theamount of money to be offered.

As the administration moved on the question ofcompensation, there were these other developments:

--The Khaleej Times in Dubai quotedunidentified salvage experts in Dubai as sayingthe Iranians recovered the flight recorder fromthe downed airliner in the past few days. ButIran's navy commander said search teams had so farfailed to find the flight recorder, Tehran Radioreported.

--With the Security Council convening today todebate the incident, the United States, Britainand France were expected to use their veto poweras permanent council members to kill any attemptto censure the United States.

Fitzwater said he would not compare payments inthe Iran airliner case with compensation theUnited States is seeking from Iraq for its May1987 attack on the USS Stark. Thirty-sevenAmerican crewmen were killed.

There have been reports that the United Statesis seeking $1 million for the families of each ofthose victims