Two leading members of Israel's parliament said yesterday after a meeting with Prime Minister Menachem Begin that if Syrian attacks against the Maronite Christians in Lebanon continue, Israel may have to intervene.

They charged Syria with using next week's Camp David summit meeting as a "cover" for the elimination of the Christian forces, assuming that Israel will not dare intervene for fear of inviting a collapse of the peace negotiations.

Moshe Arens, head of the foreign affairs and defense committee of parliament, charged the Carter administration with providing "at least tacit support to the Syrian presence in Lebanon.

"And I think this tacit support, to some extent, is responsible for the irresponsible acts by the Syrian army in Lebanon," Arens said.

Yigal Allon, former foreign minister and chairman of the subcommittee on Lebanon, said, "I think the Syrians should realize they are pushing too far . . . As much as we want to avoid any military confrontation, it's beyond what we can accept."

He urged "important international powers" - specifically mentioning the United States, France and the Vatican - to "persuade Damascus to stop his violation and stop the killing."

Both parlimentary leaders made their remarks to reporters immediately after discussing the Lebanese situation with Begin, who they reported was "very deeply concerned" about the latest Syrian moves.

A Foreign Ministry spokesman said Arens' remarks about the danger, while not representing official government policy, "carry considerable weight" because of his stature in Israel's ruling party. Allon is a leader of the opposition Labor Party.

The warnings underscored a growing dilemma for Israel as the Camp David summit meeting nears: If Israel intervenes in Lebanon, it could give Egyptian President Anwar Sadat to pretext for scuttling the Camp David talks and thereby intensifying world opinion against the Begin government as expansionist minded.

If Israel does nothing, however, there is an increased likelihood of not only the destruction of the Christian military capability in Beirut and the Maronite hill country to the north, but of increased Syrian influence in the are Israel occupied during the invasion of Lebanon last March.

Moreover, a lack of response by Israel would likely to raise the prestige of Syria in the Arab world, although Arens said in an interview published yesterday in the Jerusalem Post that Sadat may not object to Israel intervention.

Arens said that the Syrians, after hammering away" with artillery at the civilian population in Beirut, have now opened up a new front with the intention of cutting off Beirut from the northern hill towns, thus causing a separation of forces."

It's possible that the Syrian army, of the Syrian president, Mr. Assad would like to use the Camp David talks as a cover . . . and while Mr. Begin and Mr. Sadat and Mr. Carter are all at Camp David discussing Middle East peace, to use the opportunity to destroy the Christian population," Arens said.

Israel has long supplied the Lebanese Christian forces with arms and money, regarding it as a surrogate defense against Syrian control of Lebanon and the certainty of increased attacks across Israel's border by Palestinian terrorists - if not incursions by the Syrians themselves.

Israeli government sources said that the Syrian strategy appears to be to destroy Christian military strength piece by piece in small towns, with the aim of closing their only port, at Jounieh.

The gradual pace of the offensives, the sources said, is designed to avert an Israeli pretext for invading Lebanon and to minimize international attelio to te Lebanese conflict.

But Israeli officials fear that once the summit meeting starts, the Syrians army, will step up the attacks in hopes of finishing off the Christian forces. Compounding the danger is the possibility that the Christians may renew the hostilities themselves, to prevent their cause from being forgotten at Camp David.

Top Israeli officials, including Begin have been holding intensive security meetings in recent weeks, including one late night session last week at Begin's home at which a mysterious visitor - said to be an Arab official - attended and then drove away. Also participating were Foreign Minister Moshe Dayan and Israeli Chief-of-Staff Rafael Eytan.

Foreign reports said that the mysterious visitor was Camille Chamoun, one of Lebanon's Christian political leaders. Israeli officials have shrouded the meeting in secrecy.

Chamoun was reported yesterday in Beirut to have said that Syria has again reinforced its positions north of Beirut and that the Christians plan to fight to the "bitter end." When asked about the Christians' ties to Israel, Chamoun reportedly said the Christians had no Israeli advisers and no Israeli personnel.

The Syrian governors, meanwhile, is said to consider itself overextended militarily in Lebanon. Reportedly it would prefer to withdraw some of the 30,000 or 35,000 troops it has there as part of a peacekeeping force sent after the civil war. It is confronted with the problem of being unable to withdraw some of its troops while Christian forces are a significant military factor, however.

Israel also has become increasingly concerned about war games being conducted in Syria by ground and air forces. Assault formations tested their "offensive capabilities" on Sunday for the second time in less than a week according to the official Syrian news agency.