Troops of the Arab peacekeeping force today began implementing a two-stage plan aimed at stricter control of the estimated 400,000 Palestinians in Lebanon, whose preserve has often led to bitter clashes.

High-level negotiations among Lebanon, Syria, the Palestine Liberation Organization and the 30,000-strong peacekeeping force reached agreement on the plan Monday.

The plan which includes a ban on armed uniformed commandos' leaving the refugee camps, and withdrawal of armed men from Southern Lebanon, has boosted hopes for peace in the country and for reconciliation between the Palestinians and the Lebanese.

Spokesmen for the Arab peacekeeping force and the PLO said the deployment of troops at two major refugee camps in Beirut today went off peacefully.

"Everything went well," the Palestinian command said. The state-run radio said troop deployment at other refugee camps in the country was also carried out successfully.

The first 15-day stage of the plan calls for restoring civilian life in 1.3 Palestinian camps throughout Lebanon.

In the second phase, Lebanese regular troops are to move into southern Lebanon, where rightist forces have been fighting leftist Palestinians. Armed men are to withdraw from the region simultaneously.

The atmosphere was relaxed today as Arab force soldiers set up check-points on access routes to the camps in Beirut and started checking vehicles and their passengers.

It was not known when the collection of heavy weapons from the camps as provided by the plan would begin. The weapons are to be removed under the supervision of the Arab force. Smaller, weapons are to be collected as well and stored inside the camps.

In a related move, Syria last night released about a hundred Palestinians and Lebanese detained during the fighting in Lebanon. About 50 more detainees are expected to be freed in the next few days.

Meanwhile, the Palestine news agency WAFA and the rightist Falangist Party radio reported that artillery duels that started last night in southern Lebanon between leftist Palestinian forces and rightist forces were continuing. Neither side reported any casualties.