Hundreds of Moslem residents fled the eastern suburbs of Sidon, in southern Lebanon, today, as Moslem gunmen and Christian militiamen fought in the first serious outbreak of sectarian violence since Israeli troops withdrew from the area on Feb. 16.

Two Lebanese Army soldiers were killed and nine wounded when Army units attempted to intervene in the fighting and were drawn into the mortar and machine-gun battle, an Army communique said.

The Lebanese Forces, the main Christian militia, which has rebelled against the Christian Phalange Party leadership dominated by President Amin Gemayel, brought in reinforcements to the predominantly Moslem suburbs and gave the residents two hours to leave.

The mostly Sunni Moslem villages are in the Awwali River valley, just east of Sidon and near a number of Christian villages in the foothills that rise toward Kfar Fallous and Jezzine to the east.

The Christian militia reinforcements came mostly from the Jezzine area, which is still under Israeli control, and Moslem leaders called the attacks an attempt to split the region on sectarian grounds and relieve the Israeli Army of pressure from Shiite guerrillas.

Mahmoud Fatih, Sidon-area commander of Amal, the Shiite guerrilla group, said, "We are sure this flare-up is deliberately timed and part of an Israeli plan to push Christians farther south to form a buffer zone for the Israelis along the border."

Spokesmen for the Lebanese Forces in Beirut said the flare-up was strictly a local matter, unconnected to the militia's rebellion against Gemayel. The militia has accused the president of encouraging Syrian power brokering in Lebanese political affairs.

Nonetheless, the new violence around Sidon is expected to fuel interreligious rivalry and possibly provoke Palestinian guerrillas entrenched in the hills east of Beirut to come to the aid of Palestinian refugees trapped in the Sidon area. Since there is a distinct demarcation line between the heavily Moslem villages in the Awwali valley just east of Sidon and the Christian villages in the hills above, there was concern in the capital tonight that Sidon could become a new focus of sectarian strife.

The Lebanese Army command said several of its positions on the eastern edge of Sidon had come under fire from the suburbs, "compelling the Army to return fire."

A Reuter photographer said that only Moslem gunmen, mostly Amal, appeared to be returning fire at the Christian militiamen, who were shooting at Army posts from suburban rooftops.

As thousands of refugees, heeding the Christian gunmen's ultimatum, fled toward the center of Sidon, most of the port city was shut down, with public buildings converted into refugee centers, as they were when Christian and Druze civilians poured into the city during the fighting in the Chouf mountains in September l983.

Sectarian leaders had attempted to nurture peace in the Sidon area, saying that it could be a model for the rest of the country in the face of Israeli predictions that the city would be plunged into sectarian bloodshed immediately upon their withdrawal a month ago.

As the battles outside Sidon continued, Lebanon's national unity Cabinet canceled a scheduled meeting in Beirut in which it had planned to discuss the week-long revolt by the Lebanese Forces. Government officials said Gemayel would go to Damascus soon to discuss the crisis with Syrian President Hafez Assad, who has deployed troops near the Christian heartland in an apparent attempt to intimidate the Christian militia rebellion leaders.