Israeli opposition leader Shimon Peres said yesterday that the Labor Alignment would oppose the Israeli government's plan to maintain troops in Lebanon for an indefinite period after the withdrawal of Palestinian guerrillas.

Israeli officials have said privately that they intend to keep their forces in Lebanon after the evacuation of the 5,000 to 9,000 Palestine Liberation Organization guerrillas trapped by the Israelis in West Beirut until all Syrian troops leave the country. A senior official indicated to reporters here last week that the Israeli occupation could continue for a prolonged period.

Peres challenged that position yesterday at a breakfast meeting with reporters and editors of The Washington Post. "We don't want to become the policeman of Lebanon under any circumstances," he said, adding later that Lebanon's internal affairs were "not our business."

The former Israeli defense minister said an international peace-keeping force, rather than Israeli soldiers, should remain to enforce a peace accord in southern Lebanon. In contrast, the Begin government has stated it wants any international troops entering Lebanon to oversee the PLO withdrawal to leave within a few weeks.

Peres, whose party has lost two successive parliamentary elections to Begin's ruling coalition, urged the Reagan administration to capitalize on the Lebanese crisis to come to grips with what he described as the major Middle East problem--the future of the Palestinian people.

"The real test of the Reagan administration, in my judgment, will be if they can work out a Palestinian solution," he said. "What you need is a rational strategy."

Peres urged the administration to pressure both the Begin government and moderate Arab states such as Jordan and Saudi Arabia to support meaningful negotiations on the question of Palestinian autonomy in the Israeli-occupied West Bank. He said moderate Arabs might prove particularly receptive to a Palestinian solution that would enhance the region's security and counter the destabilizing threat of Moslem fundamentalists in Iran.

He implicitly criticized the United States for not opposing in the past Begin's policy of promoting Jewish settlements in the West Bank, where 1.3 million Palestinians live.

"I'm not sure the Reagan administration had a clear Palestinian policy," said Peres, adding that U.S. officials seemed to have concluded that the Palestinian problem was "insoluble" and therefore allowed Begin to operate without criticism.

The Labor Alignment leader said a solution to the Palestinian issue was "achievable." But he warned that U.S. policy-makers must find an answer that is in the interests of both the Israelis and the Palestinians, and not attempt instead to impose a solution that Israel would find unacceptable.

"You must work out a policy that Israel can live with--not a punishment," said Peres, who said all parties, including the Israelis, would have to be prepared to make sacrifices for peace.

As for the future of Lebanon, Peres suggested that the most viable solution would be for the country to be partitioned and return to its smaller, post-World War I borders, although he indicated that it was up to the Lebanese, not the Israelis, to decide the issue. The predominantly Moslem east would be separated, under such a plan, from the predominantly Christian west.

Peres said he had "mixed feelings" about the Israeli invasion of Lebanon, but criticized Defense Minister Ariel Sharon, the operation's architect. He said Sharon had erred militarily in not seizing Beirut during the first days of the invasion, rather than laying siege for eight weeks and had overestimated the military strength of Israel's Lebanese Christian allies.

Peres also said of the hard-line defense minister, "Sharon knows the strengths of military policy, but he doesn't know its limitations."

Sharon's opposition to the diplomatic mission of U.S. special envoy Philip C. Habib, Peres said, was based at least partially on "our own intelligence estimates that the PLO was stalling for time and using Habib." Peres' own assessment was that Habib, while a "very talented negotiator," faced "an impossible task . . . . It's like playing simultaneous chess with 15 untrained players."