Exploding tank shells and mortar rounds rumbled through Beirut's southern suburbs again Saturday as Hezbollah gunmen, led by Iranian revolutionary guards, fended off a drive by the pro-Syrian Amal militia to overrun their strong-holds.

The 2-day-old battle between the rival Shiite Moslem groups was the worst round of fighting in Beirut since Syrian troops arrived in the Moslem half of the capital 14 months ago.Preliminary hospital reports put the toll at 65 dead and more than 100 wounded, with most of the pro-Iranian Hezbollah's casualties still trapped inside the densely populated neighborhoods of Haret Hreik, Bir Abed and Hay Madi.

There were intensive contacts among the Amal leadership, Hezbollah spiritual leader Sheik Mohammed Hussein Fadlallah, the Iranian Embassy and Syrian military observers trying to stop the fighting.

Late Saturday night an Amal official said Hezbollah had sent a written commitment to the Iranian Embassy to stop the street combat, but Hezbollah sources said the details of a truce with Amal had not yet been worked out. At least three cease-fires have been broken in the last 48 hours.

Earlier, about 5,000 Amal fighters readied for fresh fighting after Hezbollah regained footholds captured by Amal Friday and managed to extend its control over a wider area in the 16-square-mile maze of squalid houses and alleys.

Amal combatants dodged Hezbollah snipers and helped one another strap on ammunition belts and fix shoulder-mounted rockets as their leader, Nabih Berri, assailed those "feigning piety," referring to the Hez-bollah fundamentalists.

Berri warned against "tampering with blood" and added that Amal was "not defeated, nor would it take defeat lightly."

"They were not satisfied by transforming the suburbs into a haven for terrorism because of the (foreign) hostage affair," Berri said in a statement about the Hezbollah group. "They want to turn the whole area into a hostage."

The Amal chief, frustrated by the unchecked growth of Iranian influence in his own community, waged a winning battle against Hezbollah last month, driving both it and Iranian revolutionary guards from southern Lebanon. Amal capitalized on local irritation at the overbearing conduct of Hezbollah extremists bent on imposing strict Islamic ways and Iranian political designs on Lebanon's Shiites.

The April showdown followed the kidnapping in February of U.S. Marine Col. William Higgins, which caused friction between the two groups. Most of the foreign hostages still missing in Lebanon are believed held in neighborhoods in the Beirut suburbs and environs to the southeast controlled by Hezbollah.

The fighting in the suburbs started before dawn Friday after three Amal fighters were shot to death in an argument with members of Hezbollah.

A senior Hezbollah source Saturday refused to give a casualty count but conceded that "many of our fighters succumbed to their wounds and became martyrs because they were unable to get medical care."

He added that Hezbollah had "consolidated its hold bit by bit and had gained ground, seizing control of the contested Ghobairi district during the course of the day."

Amal security sources said about 500 Iranian revolutionary guards expelled from southern Lebanon have been commanding Hezbollah's fighters. There are more than 1,000 revolutionary guards in Lebanon, and Shiite Moslem residents from the suburbs confirmed that the guards operate a training base for Hezbol-lah militants in Hay Madi.