BEIRUT, Lebanon (AP) _ Soldiers opened the main crossing point between Beirut's Moslem and Christian sectors Friday and motorists surged through it, ignoring the occasional grenade and the pepper of sniper fire across the line.

The reopening of the Museum Crossing to civilian traffic in early afternoon was arranged by a security committee made up of warring Christian and Moslem militias and the army. The crossing, named for the shell-gutted National Museum nearby, has been closed since April except for brief intervals.

Lebanon's overall security committee, which has arranged a Syrian-sponsored truce between militias in Moslem west Beirut that began July 16, met to work out a plan for protecting Westerners from being abducted near the American University of Beirut.

Many Lebanese travel between Christian east and Moslem west Beirut only when the boulevard at the museum is open, since the two alternatives are narrow sidestreets in which gunmen often lurk.

Soldiers set up checkpoints on both sides of the crossing and French truce observers monitored traffic. The 58-man French team has been stationed at the nearby Palais des Pins on the dividing line since April 1984 to oversee a cease-fire declared at that time in Lebanon's decade-long civil war.

The crossing was closed in April when the latest round of factional warfare began in the southern port of Sidon and spread to the capital.

Several attempts have been made to reopen it, but none lasted for more than a few hours because of small-arms and shell fire across the line.

On Friday, rival snipers traded rounds from vantage points on either side of the line and grenades were fired. Police said there were no reports of casualties.

In west Beirut, the security coordinating committee discussed arrangements for the protection plan at the American University and its adjacent hospital, which are in the Moslem sector.

Defense Minister Adel Osseiran said after a meeting with the committee Thursday that army patrols would be assigned to keep gunmen away from the institutions.

Fourteen foreigners, seven of them Americans, have been kidnapped in west Beirut since March 1984. Three of the missing Americans were officials of the university or hospital.