Iraq's Republican Guard, eight elite divisions of about 14,000 troops each, has emerged after four days of bombing as a pivotal target of United States-led forces in the Persian Gulf.

Pentagon planners and senior U.S. officials described the Guard units, comprising fewer than a fifth of the 545,000 Iraqi troops in the Kuwaiti theater of operations, as a "center of gravity" -- an essential source of enemy strength and balance. Though far removed from the front lines near the Kuwait-Saudi Arabia border, their destruction or dispersal from the air is at the heart of the allied strategy for avoiding -- or winning -- a ground war.

The U.S.-led air attack focused heavily in its first days, as planners said it had to do, on establishing superiority in the skies. Achievement of that objective by the end of the week, Lt. Gen. Thomas Kelly told reporters, gave allied air forces the freedom to strike any targets they chose.

They chose, among other things, to begin "concentrating on the Republican Guard," Gen. Colin L. Powell, chairman of the Joint Chiefs of Staff, said Saturday. Col. Manfred Rietsch, who commands a wing of Marine Corps F/A-18s in Saudi Arabia, told pool reporters there that his planes were subjecting the Guard to "a constant, continual bombing with no letup." By last night, officials said, more than 1,000 sorties had pounded the elite divisions.

"If it goes on for four to five days and the Guard doesn't start to move, break up or surrender, we are in for a long war," said a senior U.S. official.

The U.S. assessment of the Guard's importance in allied plans grew out of five months of analysis since the August invasion of Kuwait and extensive previous reviews of the Iran-Iraq war. Pentagon officials and unclassified military studies said the 108,000 to 110,000 guards are not only Iraq's "finest fighting troops," as Gen. H. Norman Schwarzkopf, the allied central commander, described them yesterday, but an important source of confidence to President Saddam Hussein.

Sometimes known as the Presidential Guard because of its original mission to protect the ruling Baath Party government, the Guard made its debut in conventional combat against Iran in 1985, according to a study by the U.S. Army War College's Strategic Studies Institute.

There it displayed the combat role it apparently intends to play against American-led ground forces. Awaiting an Iranian offensive near Qurnah, between the southern city of Basra and the capital of Baghdad, mobile Guard units counterattacked "with efficiency and crushing impact," according to a second U.S. study.

After a major defensive setback in 1986, when Iran broke through Iraqi lines and occupied the southern tip of Iraq's Faw Peninsula, Saddam appointed Gen. Hussein Rashid al-Wendawi to oversee a massive expansion of the Guard. Stephen C. Pelletiere and Lt. Col. Douglas V. Johnson Jr., authors of the war college study, credit Rashid with paving the way for a string of Iraqi successes that began with the recovery of Faw in 1988 and culminated in Iran's military collapse.

When the American-led coalition surprised Saddam by aggressively resisting his occupation of Kuwait, analysts said, Saddam made two significant moves. First he pulled back his Guard units, which had spearheaded the invasion of Kuwait, and stationed them as an operational reserve along the border with Iraq. Then he fired his army chief of staff and replaced him with Rashid, widely regarded in the West as Iraq's most capable commander.

One of the best-educated and most highly skilled armies in the Middle East, the Guard is organized as a mobile counterattack force of three armored divisions, four infantry divisions and one special operations division, according to a senior U.S. official. Officials said the Guard comprises self-contained fighting units, with all the elements necessary for offensive or defensive operations, including ground troops, army aviation, reconnaissance, medical support and supply and transportation companies.

The armored divisions field many of Iraq's best main battle tanks, the 500 Soviet-built T-72s that are regarded as a match for American M1A1s. The infantry are backed by powerful concentrations of artillery.

"Constantly singled out for praise" by Saddam, the Guard units are well-paid and highly motivated, according to Pelletiere and Johnson. The study they wrote said the average soldier sees himself "as the inheritor of an ancient tradition of war-fighting -- the Iraqis primarily spread the might of Islam in the 7th century."

Saddam has deployed the Guard in a crescent along the Kuwait-Iraq border, well to the north of allied troops, according to intelligence sources. Their mission is to await an allied break through the extensive network of Iraqi fortifications along the southern and western borders of Kuwait. Using a well-designed network of roads and supply dumps, U.S. officials said, the Guard plans to counterattack while allied ground troops are bogged down in a "kill sack" of sand berms, minefields and oil-filled trenches.

U.S. planners, however, say they understand Saddam's game plan and intend to disrupt it.

"I can assure you that when and if we have to fight a ground war, I'm not going to fight his war," Schwarzkopf said yesterday. "He's going to fight our war."

Schwarzkopf said the Guard units, now well dug in, would have to expose themselves to further attack from the air in order to reach advancing allied ground forces.

"You know, you can't hide in a desert, particularly when you're on the move," he said. "You leave a long plume behind you."

Meanwhile, according to other U.S. officials, allied warplanes are pounding the Guard's corps and division command posts and attempting to disperse smaller units from their commanders. U.S. analysts believe brigade-size and smaller units fight poorly without higher direction. Powell told senators in a briefing last week that the air attacks were "shaping the battlefield" to allied advantage.

"The hope, and it's only a hope, is that we can disable them so much that they will become combat-ineffective," a senior Pentagon official said.

There are doubts among some planners that a force so large and powerful can be damaged that badly from the air, and officials said the "battle damage assessment" on missions already flown has been hampered by cloud cover and darkness.

Alarmed by early exaggerations broadcast in television reports, officials are careful to downplay any claims that the Guard has been routed already.

"I was in stitches" at one televised report, said a Pentagon planner. "My 16-year-old smelled out that in the dark after a B-52 strike, it's very hard to tell whether you've 'decimated' somebody."

Schwarzkopf, in an interview yesterday, said it would be an overstatement to assert that "we're pummeling the Republican Guard."

There is little doubt, on the other hand, that that is the allied intent. Early defeat of the elite Guard, officials said, would reverberate through to the front-line troops and beyond.

One government expert, asked how Saddam personally would regard the defeat of his Guard, replied simply: "It is considered his best force. Draw your own conclusion."