Iranian Army units supported by jet fighters and helicopter gunships today gained control of the Kurdish capital of Mahabad after an assault on rebel positions, the government radio claimed today.

Armored and infantry units of the 64th and 81st divisions sent from the northwestern town of Orumieh in the afternoon reportedly broke through Kurdish defenses, which had been subjected to artillery and aerial bombardment.

The Army, which according to the official broadcasts had no casualties, said it had taken over the Mahabad barracks seized by the Kurds several months ago. But correspondents reported from the city that the troops were occupying only the outskirts of Mahabad, apparently preparing to move into the rest of the town in force Tuesday morning.

The loss of Mahabad would represent a blow to the prestige and morale of the autonomy-seeking Kurds, but would not necessarily impair their fighting ability, political analysts in Tehran said. On the contrary, they said, it could mark the start of a long, drawn-out guerrilla campaign against the central authorities.

The Kurdish rebellion represents the greatest potential threat to the government under Ayatollah Ruhollah Khomeini, the country's de facto chief of state. Khomeini appears to have made crushing Kurdish opposition his top priority and, declaring himself military commander-in-chief for the purpose, last month committed the bulk of Iran's tattered armed forces to that effort.

With the military buildup around Mahabad in recent days following Khomeini's orders for the destruction of Kurdish resistance and the execution of rebel leaders, Kurdish sources indicated that they would not seek to defend Mahabad but would take to the nearby mountains.

Many of the Kurdish guerrillas, said to be equipped with artillery, antiaircraft batteries as well as modern automatic weapons, were reported to have pulled out of Mahabad taking heavy military equipment with them.

Kurdish sources have suggested that the guerrillas may make a stand near the border town of Sardasht, where they believe the mountainous terrain would impede deployment of government tanks and put the rebel forces on a more equal footing with the Army.

The Army has said, however, that it also captured the town of Baneh southeast of Sardasht today. Like Sardasht, Baneh is a Kurdish mountain stronghold, the passes to which might easily have been defended by guerrilla units.

Official radio reports that have yet to be confirmed claimed that troops entered Baneh shortly after the capture of Mahabad, also without facing any significant resistance.

Another border town, Piranshahr, was reported captured by the government yesterday after fighting which government officials said, inflicted heavy Kurdish casualties.

The Army's apparent successes may remove whatever slender hopes remained among the Kurds for a negotiated settlement of the conflict.

A Kurdish delegation that visited Tehran in an attempt to get peace talks going announced today that it was giving up efforts to press demands that included an immediate cease-fire and the withdrawal of government forces to their main bases.

Support for a cease-fire and peace negotiations had come only yesterday from Iran's number two religious leader, Ayatollah Kazem Shariatmadari.

The commanders of the 64th Infantry Division and the 81st Armored Division were quoted on the state radio as saying government forces had "victoriously" entered Mahabad and had been "welcomed by the people," evidently depriving the rebels of their main urban stronghold.

However, an Associated Press correspondent reported from Mahabad that there was no sign of Army troops in the area of the city's main square, and several armed Kurds could be seen in the streets in the vicinity.

Heavy exchanges of artillery fire could be heard into the night echoing through the nearby hills, AP said. Government tanks fired salvos into the main body of Kurdish forces retreating toward the mountain stronghold of Sardasht, 50 miles to the south close to the Iraqi border.

Another column of troops advanced through the city's southern approaches and arrived at the outskirts of the city at nightfall.

Government commanders claimed there were no casualties among their troops, but that the rebels suffered an undetermined number.

"Now we are going to concentrate our forces in Sardasht where they can't use their tanks so effectively," a ranking official of the banned Kurdistan Democratic Party told AP. He vowed the Kurds would deliver a "severe blow" to the Army at Sardasht.

Before the fighting erupted Monday, many of the estimated 10,000 guerrillas and most of the city's civilian population of 100,000, including women and children, left Mahabad. Civilians carried as many personal belongings as they could, and the Kurdish rebels took artillery pieces and other heavy weapons with them.