Each evening this week Christian and Moslem Lebanese factions, joined at times by Palestinians, have contributed to the tension that permeates this Bekaa Valley city with bloody skirmishes anticipating the resumption of Lebanon's civil war whenever the Israelis and Syrians pull their armies out.

Their maneuvering may be premature. It is the tragedy of war-torn Lebanon that "no one in Baalbek believes this war or the fighting has ended with the current cease-fire," said Baalbek's government hospital director, Dr. Jafar Omeiri. "I think the war will eventually come back into Bekaa Valley and Baalbek," Omeiri said, sadly shaking his head.

Omeiri was not referring to Lebanon's own unresolved civil war, which is one of small arms and mountain skirmishes, but rather to a major conflagration between the massed Israeli and Syrian armies.

Around Baalbek and along the floor of the valley, the area bristles with bivouacked Syrian troops, Syrian antiaircraft gun emplacements and Syrian tanks in the potato fields. Syria also has massed hundreds of tanks along the Syrian-Lebanese border southeast of Baalbek and west of the crossroads town of Chtoura along the Beirut-Damascus road facing Israeli positions.

In five days of fierce fighting last week, the Israelis captured a section of the Beirut-Damascus road close to the Beirut end. Since the cease-fire that began last weekend, the Israelis have allowed people fleeing Beirut to pass through their roadblocks up until noon today. The refugees have then passed through Syrian roadblocks, down into the Bekaa Valley and gone on to the Syrian capital of Damascus or flocked here, overwhelming already hard-pressed facilities.

Large numbers of Lebanese and noncombatant Palestinians fled Beirut this week in response to leaflets dropped by Israeli aircraft warning civilians to leave the encircled Lebanese capital. In tension-filled negotiations this week, the Israelis have been demanding that the armed fighters of the Palestine Liberation Organization vacate besieged West Beirut and leave Lebanon.

The Israelis also have demanded that the Syrians leave Lebanon, something the Syrians have rejected. Damascus thinks of Lebanon's Bekaa Valley, where most of its 40,000 Lebanese-based troops are located, as its first line of defense. The valley's irrigated crops are also the Syrian capital's major source of food.

A trip through Bekaa from Damascus by taxi today revealed a fatalistic resignation among the people here that the Israelis will turn toward this sunny valley after they have dealt with the PLO in Beirut.

In readiness for another round of fighting, Syrian military vehicles, smeared for camouflage with the orange-red dirt of the valley, dominate the road traffic from Damascus. Yet, the customs check at the Syrian border post was cursory, as if any lull in the Middle East's perpetual state of war is a perfectly reasonable time to conduct business as usual.

Inside the Lebanese customs building at Massnaa, war's ubiquitous opportunists flocked around arriving cars waving fat stacks of green Lebanese currency and shouting, "Change money, monsieur."

The central business district of the small town of Chtoura was bombed and leveled by Israeli aircraft a week ago Wednesday before the cease-fire. It had been the headquarter of Syrian forces.

Taxi driver Fuad Said drove slowly through the crowd and turned north onto the main road leading through the Maronite Christians' stronghold of Zahle on the way to Baalbek.

A Syrian special forces soldier stopped us at a roadblock after a short distance and explained to Said that as he was a Syrian Moslem the Maronites would probably shoot him if we went that way.

We made a wide detour to get around Zahle and drove up a narrower, heavily traveled secondary road to Baalbek.

In Baalbek, the proprieter of the 108-year-old Hotel Palmyra nervously gave us instructions on how to get to the government's hospital. The front of the Palmyra is dominated by 2,000-year-old Roman temple ruins. A short distance away, a color wall poster of Iran's Ayatollah Ruhollah Khomeini prominently displayed inside a melon shop indicated some of the Islamic ferment bubbling up in Lebanon.

"This is a very complicated country," said a European doctor working with refugee relief efforts in Baalbek.

"Take away the Israelis and the Syrians and you have no unanimity among the Moslems here. You have the Moslem and Christian Lebanese ready to begin again the civil war and all of them wanting the Palestinians out," added the doctor who declined to be identified. "Everybody here is nervous."

About 30,000 refugees from Beirut, two-thirds of them reportedly armed Palestinians, have boosted Baalbek's population to an estimated 145,000 and have put a strain on the city's meager resources. The small, two-story hospital is badly overcrowded with 100 seriously wounded civilians injured when the Israelis first bombed the Bekaa in early June.

"We received 350 wounded, but those who did not have to be operated on were sent home," said hospital director Dr. Omeiri. "A volunteer German team of surgeons came in and did 86 operations in 48 hours."

"It's you Americans who have armed the Israelis who have done this," Omeiri suddenly blurted out. Later he said in a calmer tone, "We were surprised by the attack on the Bekaa. We don't know if we can cope with another one."