Israel issued a new warning yesterday that President Reagan's repeated praise for a Saudi Arabian plan is endangering the Middle East peace process by giving Israelis and Arabs the impression that the United States is tilting toward the Arabs at Israel's expense.

That was the message given to Secretary of State Alexander M. Haig Jr. by six members of the Israeli Knesset (parliament) sent here by Prime Minister Menachem Begin to dramatize his government's concern about recent statements by Reagan.

The bipartisan group is headed by Moshe Arens, who is expected to become the Israeli ambassador here shortly. After the the meeting with Haig, Arens told reporters that recent U.S. statements and actions "could reverse the peace process it took us 30 years to get going."

Arens, chairman of the Knesset's foreign policy and defense committee, caused a stir by his reference to one part of the eight-point Saudi plan that some interpret as implying eventual Arab recognition of Israel. "You might say that this is a step ahead," he said.

That caused a flurry of speculation about whether he was signaling a more flexible Israeli attitude toward the plan proposed by Saudi Crown Prince Fahd. Israel has rejected the plan in its entirety and characterized it as a blueprint for the destruction of the Jewish state.

However, in an interview last night with The Washington Post, Arens and another delegation member, former U.N. ambassador Chaim Herzog, denied any intention to soften Israel's blanket condemnation of Fahd's proposals.

"Anyone who got that impression misunderstood," Arens said. "I told Secretary Haig that the kind of American response that would have been healthy would be to tell the Saudis that they have some way to go, that they should sit down to negotiate with Israel without preconditions."

Arens noted that Fahd's plan does not mention Israel by name and speaks only of conceding the right of states in the region to exist if Arab conditions are met.

"Saudi Arabia has to learn to pronounce the name of Israel," he said.

Herzog, a member of the Labor Party opposition to Begin's conservative Likud Party, charged that the Saudi plan is a ploy to pressure the United States into dealing with the Palestine Liberation Organization.

Since U.S. policy is to refuse to talk to the PLO as long as it rejects Israel's right to exist, Herzog continued, the Saudi aim is to give Washington a back-door approach to the PLO by creating the impression that the PLO has met the U.S. requirement through endorsement of Fahd's plan.

Within Israel, both men said there is increasing concern that the United States seems to be favoring the Saudi plan at the expense of the 1978 Camp David accords. At the same time, they added, each time Reagan or other administration officials speak favorably of the Saudi plan, it fuels a perception among Arab governments that the United States is backing away from Camp David and reduces their incentives to come to terms with Israel.

The Camp David agreements, which produced the Egyptian-Israeli peace treaty and now are focusing on achieving self-rule for Palestinian inhabitants of Israeli-occupied territories, call for negotiated settlement of various disputes between Israel and the Arab world.

The Saudi plan, by contrast, sets forth as its starting premise a demand that Israel withdraw from all occupied Arab territories including East Jerusalem, that a Palestinian state be established in some of these territories and that Palestinians be allowed to return to their homeland in what is now Israel.

Israeli concern about U.S. intentions increased during the recent congressional battle over Reagan's decision to sell an $8.5 billion package of sophisticated aircraft to Saudi Arabia. It reached almost unprecedented heights when Reagan, immediately following his victory on the aircraft sale, lauded the Saudi plan because he said it implied recognition of Israel.

Since then, administration officials have gone to great lengths to reassure the Israelis that Camp David remains the cornerstone of U.S. Mideast policy. Reagan apparently exacerbated the situation again at his news conference Tuesday when he said he believes the Saudi plan involves "implicit recognition of Israel's right to exist as a nation."

"When seen through Saudi eyes, such statements appear to support their position and give them reason to be more intransigent," Arens said.