Lebanon, whose many sectarian and political factions have feuded for decades and fought a civil war in 1975-76, remains an arena for a variety of military and paramilitary forces.

Those caught up in the current warfare in and around Beirut include the following:

Multinational Peace-keeping Force--It was formed a year ago with 2,000 troops from the United States, France and Italy for the purpose of overseeing the evacuation of the Palestine Liberation Organization fighters from Beirut. It originally was to have been disbanded 30 days after the PLO's departure.

The multinational force now has grown to about 5,350 troops--1,200 U.S. Marines, 2,050 Italian and 2,000 French troops and a 97-man British armored car squadron. In a support role off the coast but not part of the force, the United States has a 1,900-man Marine task force and several vessels and the French have the aircraft carrier Foch.

When the multinational force was formed, the State Department said it would "operate in and around the Beirut area" and would "take up positions and operate from locations determined by mutual agreement between various national contingents and the Lebanese Armed Forces." The State Department said then that "there is no intention or expectation that U.S. forces will become involved in hostilities in Beirut."

Lebanese Army--Lebanon has rebuilt its Army largely from scratch after it broke apart during the 1975-76 civil war. On paper, it has about 24,000 troops but most analysts put its actual fighting strength at much less. U.S. Army Col. Arthur Fintel, in charge of the American effort to rebuild the Lebanese Army, said recently that it can now field 14,000 men in tactical units plus 10,000 in support units.

Fintel has cited lack of experienced officers, poor logistical support and bad use of equipment as the Army's weaknesses. The United States is spending $150 million to train and equip the Army and has sold it 34 M48 tanks, 107 armored personnel carriers and machine guns in the past year. Lebanon is being encouraged to form an Army of light infantry companies rather than major fighting capabilities such as those of Israel or Syria.

The enlisted men are about 60 percent Moslem and 40 percent Christian. The officer corps has more Christians, ranging from a 70-30 ratio among majors to a 50-50 ratio in the top ranks. The Army has no draft and relies on volunteers.

Lebanese Forces--The largest Christian militia, of which about 80 percent is from the right-wing Phalangist Party. Although it was headed by his slain brother Bashir, President Amin Gemayel has no direct control over the Lebanese Forces and his ties with them have been ambiguous. The militia has been blamed for the massacre at the Palestinian refugee camps last year but denies responsibility.

It has a standing militia of about 10,000 plus about 15,000 reservists and operates on an annual budget of about $190 million, raised by taxes in some areas it controls, which include east Beirut, coastal sections north of the capital and mountains to the north and south and areas in central and southern Lebanon.

Press reports say the Lebanese Forces got $15 million worth of captured PLO arms from Israel and now have 50 to 60 tanks, heavy and long-range artillery and armored personnel carriers.

Druze--A breakaway sect of Islam and traditional foes of the Christians, the Druze make up about 10 percent of Lebanon's population. They are concentrated in villages in the Chouf mountains southeast of Beirut and also live in areas of the Upper Metn mountains northeast of the capital and sections of southern Lebanon.

The militia, allied with leftist Moslem militias and Communist groups, has an estimated 4,000 fighters. Those in the Chouf are heavily armed, largely by Syria but, according to Phalangists, they also have been aided by Israel.

Amal--It is both a leftist party and the militia of the Shiite Moslems, who make up about 30 percent of Lebanon's population. It claims to take no foreign support, existing solely from contributions, but western diplomats say it gets arms from Syria and Iran and support from the Soviets.

Amal, which controls sections of southern coastal Lebanon, west Beirut and suburban areas, and Baalbek in eastern Lebanon, says it has 100,000 militiamen; Western diplomats say it has fewer than 10,000 trained troops. It has surface-to-surface missiles, mortars, long-range artillery and truck-mounted guns.

Mourabitoun--The militia of the Sunni Moslems, who also make up about 30 percent of the country's population, has its headquarters in west Beirut and is also active south of the capital.

It has about 5,000 militiamen and is heavily armed, with Soviet-made antiaircraft missiles, rocket launchers and tanks that Mourabitoun spokesmen say were bought on the international black market but some analysts believe came from departing PLO fighters last year.

Syrians--The Arab League formed an Arab Deterrent Force in 1976 to end Lebanon's civil war and the force was made up largely of Syrian Army troops. Between 25,000 and 35,000 are still there, most of them in the Bekaa Valley and in northern Lebanon, including Tripoli. Last week the Lebanese government formally asked the Arab League to withdraw the deterrent force.

Palestinians--Only a small number of Palestinian forces remain in Lebanon since the evacuation of most of them from Beirut. About 6,000 are in the Bekaa Valley, with Syrian-backed factions fighting factions loyal to Yasser Arafat, and 2,000 are in the Tripoli area.