Former Lebanese president Camille Chamoun has said that elections to choose Lebanon's next president, who is scheduled to take office in September, cannot take place until the crisis over PLO guerrillas in West Beirut is resolved.

In this country, deeply torn by foreign military intervention and its own bloody domestic conflicts, the method and timing of the presidential elections will have a profound effect on political stability. The presence of foreign armed forces is intricately tied to the domestic political outcome.

The most recent Israeli bombing and ground attack against largely Moslem West Beirut may already have upset the Christian-Moslem equilibrium that will be needed for the country's political leadership to rebuild the shattered government, one prominent Christian politician said today.

In a further development, another Christian leader disclosed that a major effort to reconcile Bashir Gemayel, rightist Christian leader and the only declared presidential candidate, with leftist Moslem leader Walid Jumblatt has failed.

Under Lebanon's constitution, parliament must elect a new president by Aug. 23 to take over one month later from Lebanese President Elias Sarkis. Sarkis has indicated that he will not stay on past the end of his term on Sept. 22, informed Lebanese sources said.

However, one of Gemayel's advisers, who declined to be identified, and Dory Chamoun, son of Camille Chamoun, disagreed in separate interviews on whether a constitutionally acceptable election can be held by the August deadline.

More important, however, both political officials expressed doubt about today's reports that the guerrillas of the Palestine Liberation Organization could begin to withdraw peacefully from their positions in West Beirut by next week.

"The PLO forces are too divided Lebanon's delicate Christian-Moslem balance broke down into civil war in 1975-1976. The PLO, which has been growing in strength inside Lebanon since the late 1960s, joined in on the Moslem side. among themselves" for PLO leader Yasser Arafat to be ready to do this, Dory Chamoun said. Chamoun, 50, a Christian who is secretary general of the National Liberal Party that his father heads, said that it will take Israeli military action to get the PLO out of West Beirut.

Camille Chamoun's statement was reported in the rightist Christian newspaper, Le Reveil. The elder Chamoun, 82, who was Lebanon's president in the 1950s, is still highly respected among Lebanese Christians and retains a measure of regard among the country's Moslems.

Lebanon's delicate Christian-Moslem balance broke down into civil war in 1975-1976. The PLO, which has been growing in strength inside Lebanon since the late 1960s, joined in on the Moslem side. The Israelis have been nominal allies of the Christians.

The Israelis stepped up their attack on the PLO guerrillas in West Beirut earlier this week with a sustained bombardment that ended in the deaths of hundreds of Lebanese and Palestinian civilians and widespread destruction in that half of the city. This could so embitter Lebanese Moslems as to affect the country's political future, Dory Chamoun said in an interview.

Some Moslems, the younger Chamoun acknowledged, see the Israelis as allies of the Christians. Their attitudes toward a reconciliation with the Christians after the PLO has left "will be determined by the next few days" of Israeli actions in West Beirut, he said. "There is still an unknown as to what the Moslem reaction is going to be," he said.

Christian Phalangist leader Gemayel, as the leading contender for president, tried to reconcile his long-held differences with Jumblatt by meeting with him last month. Soon afterward, however, the Gemayel adviser said, Jumblatt flew off to a meeting with Syrian president Hafez Assad in Damascus and "violently" criticized Gemayel's presidential candidacy as having the support of "Israeli tanks."

There have been no new attempts at bringing the two men together, the adviser said. "With the mentality of Jumblatt, it is useless," he said.

Besides leading a leftist coalition called the National Movement, Jumblatt is one of the Moslem Druze sect's traditional leaders.

The Christian-Druze relationship, after years of mutual distrust and killings, "is very important" to Lebanon's future stability, Dory Chamoun said.

"To what extent the Druze would back Gemayel as president is still a large question," he said. "Bashir is going to have a very difficult time being accepted by them."

Gemayel's political adviser said that he felt the crisis in West Beirut would be ended militarily by the Israelis before Aug. 23. Dory Chamoun also predicted that the crisis would be resolved by military means but not until Sept. 23, inaugural day.