The nation's two top military leaders, in a closed-door report to Congress yesterday on the three-week-old Persian Gulf War, left a strong impression that an allied ground offensive is not imminent, House and Senate members said.

Defense Secretary Richard B. Cheney and Gen. Colin L. Powell, chairman of the Joint Chiefs of Staff, offered no timetable for such an attack but assured lawmakers -- virtually all of whom said they favor continuation of the current bombing campaign -- that the Bush administration is pleased with the course of Operation Desert Storm and not eager to move the war from the sky to the ground.

"I really feel good," said House Minority Leader Robert H. Michel (R-Ill.), after listening to the briefing by Powell and Cheney. "There's no rush to do it."

Sen. J. James Exon (D-Neb.), a senior member of the Senate Armed Services Committee, agreed. "I do not get the impression that a ground war is imminent."

The trip to Capitol Hill by Powell and Cheney, who depart today for a gulf visit to gauge the war's progress, came as waves of U.S. B-52s and other bombers struck Iraqi Republican Guard positions every three or four hours yesterday. But allied officials, other than suggesting Iraqi soldiers are getting little sleep, offered scant evidence that the raids are substantially weakening the Guard and appeared to give contradictory reasons for the relentless bombardment.

As the third week of the Persian Gulf War came to a close, the allied air campaign -- now approaching 50,000 sorties -- focused on the Guard's tanks, artillery, supply depots and command headquarters. The 150,000-member Guard serves as President Saddam Hussein's strategic reserve; as Iraq's best-trained and best-equipped fighting force, it is considered the critical linchpin in the Iraqi military.

"We're out there to destroy the Republican Guard," Marine Brig. Gen. Richard I. Neal told reporters in Riyadh, Saudi Arabia, yesterday.

But Group Capt. Niall Irving, spokesman for British forces in Operation Desert Storm, seemed to contradict this stated aim by insisting the bombardment of the Guard is "designed basically to lower his morale . . . not to try and wipe out the Republican Guard. It is to reduce their capability to fight effectively, to minimize our casualties."

Further confusing the issue was an assertion yesterday by Gen. Michel Roquejeoffre, commander of French forces in the Persian Gulf, that the Guard "has been diminished by around at least 30 percent." A similarly optimistic estimate came yesterday from official Israeli sources who said that at least one of eight Guard divisions had been badly mauled, with 600 Iraqi tanks and more than 10 percent of Iraq's ammunition stockpile destroyed in the bombing.

"We believe that there has been damage done to the Republican Guard," Lt. Gen. Thomas Kelly, senior operations officer for the Joint Chiefs of Staff, later told reporters at the Pentagon. But citing difficulty in assessing damage to entrenched troops and a desire not to "tell the enemy exactly what we know," Kelly declined to provide further details.B-52s Continue Hammering

A Pentagon official said about 50 B-52s -- flying from England, Spain, Saudi Arabia and the Indian Ocean island of Diego Garcia -- are hammering the Guard and gradually reducing Iraqi antiaircraft guns to permit lower-flying warplanes -- such as A-10 Warthogs armed with Maverick missiles -- to "kill the tanks one by one." U.S. intelligence officers who briefed the House Permanent Select Committee on Intelligence yesterday said Iraqi forces based in Kuwait are running low on food and fuel, according to a government official; 20 days ago it was believed that they had only a one-month supply of those two crucial commodities, the official added.

Iraq, which previously had announced 428 civilian deaths from the allied raids, yesterday significantly increased that number by stating that about 150 people, including 35 children, were killed in an allied attack on the southern city of Nassariyah. The government daily newspaper Al-Thawra also reported that 349 people have died in the southern port city of Basra, the country's second largest city and gateway to Iraq's army of occupation in Kuwait.

In Baghdad, apparent strikes with Tomahawk cruise missiles knocked a 50-yard section of the key Jumhouriya Bridge into the Tigris River yesterday. A broadcast by Baghdad radio yesterday accused the allies of trying "to expel Iraq from the 20th century," by targeting scientific, economic, cultural, medical and residential areas.

President Bush, speaking to the Economic Club of New York, said last night he was "annoyed at the propaganda coming out of Baghdad" suggesting that allied bombers had struck numerous civilian targets. The allied air campaign, he said, "has been fantastically accurate."

Continuing to pursue the possibility of a diplomatic settlement of the war, senior Soviet and Turkish envoys met in Tehran yesterday with the Iranian foreign minister. But there was still no reported Iraqi response to the peace "ideas" that Iran offered earlier this week.

Jordan's King Hussein, who has increasingly been a Baghdad partisan in the war after many years as one of the West's closest Arab allies, yesterday tilted even further toward the Iraqi camp. "This war is a war against all Arabs and all Muslims and not against Iraq alone," the king declared, while calling for broad support for Iraq.

Bush, asked for comment while on Air Force One en route to New York, said: "I think {the Jordanians have} made a mistake to align themselves so closely with Saddam Hussein against the rest of the world. But on the other hand, I have tried to understand the pressure that King Hussein is under. So we will obviously try to keep open lines of communication."

In a brief overview of allied progress in the air war, Neal told reporters in Riyadh that at least 42 Iraqi bridges have been attacked and "apparently have suffered major damage. We calculate that at least 70 percent of his lines of communication have been in some way disrupted."Iraqi Jets Shot Down

U.S. intelligence analysts have confirmed that 10 more Iraqi planes fled recently to Iran, Neal said, bringing to 120 the number seeking sanctuary there. Two others trying to flee -- SU-25 Frogfoot bombers -- were shot down by a pair of U.S. F-15s, which "probably" also destroyed two MiG-21 fighters, Neal said.

The two American pilots, identified in a pool report by their radio call signs of "Vegas" and "Gigs," told a reporter that they were certain the MiGs had been destroyed. "They knew that they were under attack from indications we had on our radar," said Gigs, a first lieutenant from Cincinnati. "It appears that they were trying to accelerate and outrun us . . . as if they were trying to beat us to the border."

Quickly closing the gap from 60 miles to seven as the desperate Iraqis dived to within 100 feet of the desert floor, the Americans fired air-to-air missiles and quickly spotted "all four fireballs," Gigs said after returning to his base -- dubbed Texas Stadium -- in central Saudi Arabia. "It was just the most spectacular thing I have ever seen."

For the third successive night, the battleship USS Missouri fired its 16-inch guns, blasting radar and artillery sites.

Although no Scud missiles have been launched by the Iraqis since Saturday, about 5 percent of the allied sorties continue hunting for mobile launchers, one of which was attacked and destroyed in western Iraq, Neal said.

Ground action remained quiet, officials said, although 17 more Iraqi soldiers were captured, including a half-dozen who surrendered in a Land Rover. Another 650 sorties struck targets in Kuwait, he added, as the search for small convoys and troop concentrations continued.

British pilots reported "some of the heaviest air defense activity put up by the Iraqis for some time," Irving of the Royal Air Force said.

Eight surface-to-air (SAM) missiles were fired unsuccessfully at one British aircraft -- a volley which the group captain said implied "that there isn't central control" over the Iraqi air defense system.

Another British Tornado barely evaded a SAM that "got extremely close indeed" before detonating "about half a mile away," he added, without speculating on reasons for the intensified defenses.

British pilots have been "selective" in attacking fuel dumps "that are perhaps close to {Iraqi} forces and easily moved," Irving added, "so that, yes, {the Iraqis} may have more than a million tons left when the {ground} campaign starts, but it doesn't really matter because {the Iraqis} can't get at it and can't transport it."

With the war entering its fourth week today, a substantial majority of Americans continued to support the administration. A new Washington Post-ABC News poll found that 78 percent of those questioned backed the decision to attack Iraq, up from 75 percent in a similar survey last week.

The strong support persists despite a growing expectation that the war will not be a short one.

Fifty-four percent of the 1,008 randomly selected adults said they believe the war will last longer than six months, up from 40 percent in a survey conducted Jan. 20.

Even a majority of those who expected a relatively long war said they support it.

That apparent satisfaction with the progress of the war was reflected on Capitol Hill yesterday, where lawmakers seemed relieved after hearing the Cheney-Powell presentation. The two Pentagon leaders provided few new details about the war other than some battle damage assessment photographs, several members said, but left the impression that they "are not impatient," as Sen. Richard G. Lugar (R-Ind.) put it.

"Our aerial bombardment continues to soften up the ground forces," while allied psychological warfare efforts have become "very active," Lugar said. Added Sen. Robert J. Dole (R-Kan.), "Everyone wants to keep hammering with air power as long as they can."Psychological State Critical

A government official familiar with the intelligence estimates that were provided the House intelligence committee yesterday said the psychological state of Iraqi ground forces is considered a critical factor -- which "we will know in a few days" -- in determining the length of the war.

The official also said there are indications of increased terrorist activity linked to the war. He said U.S. intelligence officials are particularly concerned that terrorists may use Sudan as a staging ground for attacks against U.S. facilities.

As they have in public pronouncements, Cheney and Powell told lawmakers yesterday that gauging the precise effect of bombing against Republican Guard units is impossible, although, according to a House member, at least one Guard division is believed to be 40 percent to 50 percent disabled.

Irving, the RAF group captain, offered several examples of why exact intelligence is hard to come by. Iraqi forces are using numerous wooden tank decoys "covered in some sort of tinfoil or something" to reflect radar and lure allied bombers into attacking, Irving said.

"They're also putting buckets of oil on top of perfectly serviceable tanks and lighting them to imply" that they have been destroyed, he added.

Gen. H. Norman Schwarzkopf, the Desert Storm commander, yesterday characterized the Iraqi enemy as beset with "the mad-dog syndrome."

"We all like to think that, you know, when we're dealing with a dangerous situation that there's a predictability there," Schwarzkopf told CBS's "This Morning." "But in a mad dog there is no predictability."

Staff writers Dan Balz, David S. Broder, Helen Dewar, Barton Gellman, Tom Kenworthy, R. Jeffrey Smith, Jackson Diehl in Jerusalem, Jonathan C. Randal in Tehran and staff researcher Lucy Shackelford contributed to this report.