The Lebanese army began deploying in both Moslem and Christian sectors of Beirut Monday, in the first phase of a plan to end the country's 15 1/2-year-old civil war.

About 8,000 troops moved in to replace the rival armed militias that completed their withdrawal Monday.People lined the streets in the Christian, eastern sector of the capital, to cheer the government troops. Women showered the soldiers with flower petals, rice and scented rose water.

The restitution of state authority is seen as a major achievement in the government's efforts to end the civil strife that has left more than 150,000 people dead.

The first phase of the plan went into effect with the completion earlier Monday of the withdrawal of all warring militias from the greater Beirut area. This extends along a 15-mile coastal strip between the Kelb River in the north and Damour River in the south.

The army started moving in after the 6,000-strong Lebanese Forces militia led by Christian warlord Samir Geagea withdrew from eastern Beirut to positions in the Christian hinterland of Kesrouan province.

The last remaining 2,000 Lebanese Forces troops rumbled out of the neighborhoods of Ashrafiyeh, Karantina and Nabaa in a convoy of 400 military vehicles. The convoy included 30 tanks decorated with colored portraits of Geagea and the militia's flag of a green cedar tree on a white background.

Some trucks towed Soviet-made 130mm howitzers and twin-barrelled anti-aircraft guns. About 1,660 tons of ammunition were taken from the city over the previous week.

"Today we complete our withdrawal from Greater Beirut which will come under the protection of the Lebanese army. We hope the army will soon be in control throughout the nation," said the militia's Voice of Free Lebanon radio.

The main Moslem Shiite and Druse militias announced last month they had completed the withdrawal of their militias from Greater Beirut.