Moshe Arens, who will replace Ariel Sharon as Israeli defense minister, said yesterday that Lebanon must establish "good relations" with Israel if it wants Israeli forces to leave, and he warned the United States that "a good dose of patience" will be required to reach a withdrawal agreement.

In an interview with staff members of The Washington Post, Arens said Israel insists that a withdrawal accord must contain some form of normalized relations between the two countries and security arrangements that he implied would provide for some Israeli military presence in southern Lebanon.

Arens, who was confirmed as defense minister by Prime Minister Menachem Begin's government yesterday, acknowledged that Israel's position has caused "a lot of impatient frustration" in the U.S. government and that "it sometimes is translated into anger."

Yet he left no doubt that, despite the tensions in U.S.-Israeli relations, the Begin government intends to hold fast to its view of Israeli interests in Lebanon and the wider Mideast peace process.

"We have waited 35 years," he said in reference to Israel's struggles with the Arab world. "We're prepared to wait another year."

However, shortly before the interview, President Reagan gave a new demonstration of U.S. impatience in a speech to the American Legion.

The president, calling for Israel, Syria and the Palestine Liberation Organization "to withdraw their forces from Lebanon in the shortest time possible," added:

"This administration is prepared to take all necessary measures to guarantee the security of Israel's northern borders in the aftermath of the complete withdrawal of the Israeli army."

Reagan's remarks seemed, at first glance, to represent a unilateral U.S. offer to ensure Israel against future attacks from within Lebanon.

However, White House officials, while not specifically ruling out the possibility of such a guarantee, said later that the president's comment should be seen in the context of previous U.S. policy statements that have noted the need for an agreement that will both protect Israel's borders and achieve the withdrawal of foreign forces from Lebanon.

"It's too early and too hard to say what we might or might not do," Mort Allin, a White House spokesman, said. In private, though, U.S. officials have made known that they believe the security problem can best be solved by putting an expanded multinational force--including American troops--in southern Lebanon.

Reagan and other senior U.S. officials also have made clear that they regard Israel's insistence on normalization of relations as an excessive demand that poses great problems for Lebanese President Amin Gemayel's efforts to unite his country and win support from other Arab governments.

Arens, the Israeli ambassador here for the past year, said he was unaware of what Reagan meant by his talk of a guarantee and added, "I would prefer not to provide my own interpretation."

"We have a long tradition that the only guarantee for Israel's borders is the Israeli Defense Forces," he noted pointedly. He also said: "Israel's experience with international guarantees has not all been good. I find it very difficult to find a single instance where it's been good . . . . "

Throughout the interview, he emphasized that the Begin government believes Lebanon will be unable for a long time to police the south without Israeli help and that "a good Lebanese-Israeli relationship is an essential building block to restoring Lebanese stability."

"The talks on Lebanon are not troop-withdrawal talks," Arens insisted, saying they "are talks as to the future relationship between Israel and Lebanon; and they contain as one component . . . the question of the arrangements that have to be put in place in southern Lebanon so that Israel and Lebanon and the United States would feel reasonably sure that once the Israeli defense force withdraws, the PLO will not come back."

He insisted that Israel has no intention of keeping 30,000 troops in Lebanon. But he also kept turning aside questions about what kind of force Israel wants to keep in southern Lebanon or what rights it might be seeking to reenter the area if it sees a threat. Such matters, Arens said, should be left for discussion at the negotiating table.

Saying it is incorrect to describe the talks as "stalled," Arens said it was "a remarkable achievement" that Israeli and Lebanese negotiators are talking to each other "in a good environment." Referring to U.S. pressures for an agreement, he said:

"What we need is a good dose of patience . . . . What you really need is a commitment to the negotiating process, not a commitment to a schedule."

He left no doubt that he regards U.S. policy concerning both Lebanon and the wider Arab-Israeli conflict as naive and dangerous to his country. He said:

"There are lots of people in the United States who look at the Middle East as if it were the Middle West or Western Europe . . . .That's a perspective that's perfectly appropriate on the U.S.-Canadian border, but it's not really very appropriate for the Middle East.

"It's characteristic of the views of many people in the United States in official positions and in private life and in the media when they talk about the Middle East. They're giving us all kinds of advice, and it's not good advice."

In response to questions about U.S. efforts to induce King Hussein of Jordan to join expanded talks on the future of the West Bank and Gaza Strip, Arens said the king "will be welcome" if he agrees to negotiate with Israel without preconditions such as demanding a freeze on Jewish settlements in the occupied territories.

But, he stressed, Israel believes the best hope for Middle East peace lies in making the Arab countries realize they have no hope of defeating the Jewish state militarily. "The first precondition is that they feel they have no military option," he said.

"If Hussein feels he has an incentive, he'll come. If he feels he has no incentive, he's not likely to come. . . . If he hasn't come to date, clearly that's his conclusion: there's nothing in it for him. Maybe he's changed his mind now."