Sweeping unopposed across northeastern Iraq, government-backed Kurdish guerrillas overran Sulaymaniyah, their rivals' main stronghold, today, and captured a key hydroelectric dam. Their advance sent thousands of the defeated Kurds fleeing toward the Iranian border.

The swift moves left the Kurdish forces that have allied themselves with President Saddam Hussein in control of most of the Kurdish-inhabited swath of northern Iraq that has been under U.S. and allied protection since just after the 1991 Persian Gulf War. They raised the prospect that Saddam's government in Baghdad -- if it continues to work in tandem with Massoud Barzani, leader of the advancing Kurdistan Democratic Party -- can move to reassert a degree of Iraqi authority over the area.

U.S. policy in the region has sought, with little success, to use the separatist Kurds and their mountainous homeland as a springboard for broader opposition to Saddam and his military in the Iraqi heartland to the south.

In coordinated actions today, one column of Barzani's forces moved on trucks from the northwest into Dukan, site of a major power-generating dam that provides electricity to the recently captured city of Irbil. A second column, driving from the east, rolled without a fight into Sulaymaniyah, headquarters of the rival Patriotic Union of Kurdistan, headed by Jalal Talabani, according to Barzani lieutenants and U.N. observers.

Ross Nuri Shaways, a senior Barzani lieutenant in charge of the western military thrust, said here that 5,000 guerrillas entered Sulaymaniyah from the east at 7 p.m. and were "warmly greeted with flowers by the population," which is estimated at 500,000.

His report was later supported by U.N. observers.

The Barzani force from the east began its drive today near the Iranian border at Halabja, where Saddam's army, in 1988, killed a reported 5,000 Kurdish civilians with poison gas while putting down an insurrection.

The force then fought an engagement with Talabani's guerrillas at Said Sadeq, a road junction town, before racing unopposed to Sulaymaniyah itself.

There was no word on the fate of Talabani and his headquarters staff. They were presumed to have fled along with thousands of his followers toward the nearby border with Iran, which has aided Talabani's faction in the past.

"I'm sure he's on his way to Iran," Shaways scoffed.

Barzani and Talabani were the main leaders of the Iraqi National Congress, a U.S.-sponsored opposition group composed mainly of Kurds but also including dissident Iraqi Shiites and secular Sunnis who had deserted Saddam's government and military in Baghdad.

Since Barzani and Talabani fell into a blood feud in 1994 -- culminating in Barzani's pact with Saddam and their attack on Irbil on Aug. 31 -- the group has fallen apart.

Although some Iraqi troops and heavy armor remain in the Kurdish-inhabited areas, there has been no sign of Iraqi participation in Barzani's military campaign since the Talabani forces were driven from Irbil with help from Iraqi artillery, armor and an estimated 30,000 troops.

No Iraqi troops or equipment were seen in the drive on Dukan. But Iraqi plainclothed security forces have remained active, reportedly rounding up army deserters and other dissidents who had joined the U.S.-financed opposition headquartered in Irbil.

As Barzani's forces closed in, thousands of Sulaymaniyah residents were reported heading to the mountains near the Iranian border, 30 miles to the east, in a small-scale echo of the 1991 exodus that followed Saddam's repression of a rebellion that broke out -- with urging from the United States -- after the Gulf War.

At that time, 2 million Kurds fled toward Iran and Turkey. The human flood led the United States and its allies to ban Iraqi flights north of the 36th parallel and launch Operation Provide Comfort to help the refugees resettle in the villages that dot the rugged border mountains near Turkey, Iran and Syria.

A radiant Barzani, who showed up here to congratulate his men on their day's work, made clear as his troops moved forward that he intends to complete his sweep of the principal Kurdish population centers in northern Iraq.

"I see no reason to stop us," he said in an impromptu meeting with his senior lieutenants under a tree shortly before Sulaymaniyah fell, "and people in Sulaymaniyah itself are asking us to come."

He was also buoyed by an impressive list of victories elsewhere.

Localities that fell today to his forces included the cities of Raniyah and Qalat Dizah, east of Irbil, and three strategic towns -- Galala, Choman and Kasri -- on or near the strategic Hamilton Road, which links Iraq's far northeast with Iran.

Asked if he had expected such a rapid advance, Barzani said, "Not at all. Yesterday we never planned to take Kuysanjaq," a city 50 miles east of Irbil. "Today our plan was to go just three miles."

Barzani said Talabani "should know himself if he is ready to admit defeat." Iraqi Kurds, he said, need new elections, "hopefully before the end of the year," to get a long-paralyzed regional government back to functioning.

About 5,000 infantrymen -- armed with weapons from rocket-propelled grenades and Kalashnikov assault rifles to truck-mounted rocket launchers and antiaircraft guns used for land targets -- moved fitfully down the road against sporadic resistance from Talabani's defenders.

Only when they came under mortar and small-arms fire did the advancing guerrillas send flanking troops off to the side to flush out their foes. Time and again, they cheered and shouted "Rayankirt!" -- meaning their foes had scampered. The guerrillas included boys still ignorant of the razor and old men who have been fighting since the legendary exploits of the late Mullah Mustafa Barzani, Massoud's father.

Their mood was jubilant. One fighter driving a pickup truck shouted to his comrades, "Hurry, hurry, hurry! Don't miss your chance for two free seats for Sulaymaniyah!"

Barzani's losses were reported as three dead and 15 wounded. At least one follower of Talabani was reported killed. Residents of villages conquered along the way, who were telling foreign visitors only three days ago that they were solidly in favor of Talabani, put out Barzani's trademark yellow flags in profusion and dug up framed pictures of Barzani.

At a deserted roadside restaurant, a middle-aged man said, "I am poor and neutral, and have nothing to do with politics."

For the advancing forces, the only major disappointment of the day concerned the Dukan dam generating plant. Local engineers said Sunday that the head of Sulaymaniyah's electricity board removed computer cards controlling power generation. Until those cards are either replenished or returned, Sulaymaniyah will get power from the Derbendikhan dam, 36 miles southeast of Sulaymaniyah, but Irbil and its surrounding province will remain without electricity. CAPTION: IRAQI FACTIONS Kurdistan Democratic Party (KDP): The largest Kurdish faction in northern Iraq. By controlling roads to Turkey and levying fees on truck traffic, the KDP has made millions of dollars taxing' illegal oil exports to Turkey and goods imported into Iraq. Headquartered in the northern Iraqi city of Salahuddin, Leader: Massoud Barzani, son of the late Mullah Mustafa Barzani, leader of a Kurdish separatist uprising in 1943. Massoud Barzani recently engineered a strategy of cooperating with Iraqi President Saddam Hussein. Patriotic Union of Kurdistan (PUK): Until Saddam's roundup of its leaders and the KDP's conquest of PUK headquarters yesterday, the PUK was the second-largest faction in northern Iraq. Headquartered at Sulaymaniyah, the PUK broke away from the KDP two decades ago. The PUK recently accepted aid from Iran. Leader: Jalal Talabani. Iraqi National Congress (INC): After the United States and its allies drove Iraqi forces from northern Iraq in April 1991, the United States sought to ease tensions among the Kurds, resulting in the formation of this U.S.-backed umbrella group of anti-Saddam factions, most notably the KDP and PUK. Fighting resumed in 1994 when the KDP refused to share its oil tax revenues with the PUK. National Accord: Formed with Saudi help in 1990 and the recipient of millions of dollars in CIA assistance. The National Accord, an exile group specializing in anti-Saddam propaganda, suffered a severe blow this summer with the capture of more than 100 persons associated with it. Its greatest assets are a dissident radio station, and backing from Jordan's King Hussein. Leader: Ayad Alawi, a Baghdad-educated doctor who was once a leading figure in Iraq's ruling Baathist Party, but who since the late '70s has been a leading critic of Saddam and an advocate of a coup to overthrow his regime. CAPTION: Jalal Talabani CAPTION: Massoud Barzani CAPTION: Some of Saddam's Kurdish allies exult as they close in on Sulaymaniyah aboard vehicle fitted with a rocket launcher. CAPTION: Kurdish guerrillas stand next to a burning house in Dukan in northern Iraq during their advance toward Sulaymaniyah.