In a preview of the tough line he is expected to take next week in talks with President Reagan, Israeli Prime Minister Menachem Begin today warned that his country will resist any pressures to force withdrawal of its troops from Lebanon unless arrangements are first made to ensure the Jewish state's security from attack.

Begin reasserted his government's insistence that a demilitarized zone, cleared of Palestinian fighters, must be created and maintained in southern Lebanon before Israeli troops will be withdrawn.

"We shall never accept a situation in which there is a return to the status quo ante," he said in reference to the pre-invasion situation, where towns and settlements in northern Israel were within range of Palestinian artillery and rockets.

"There must be an area of from 42 up to 48 kilometers that separates us," Begin said. "As long as this is not achieved, the Israeli army will stay. I would like our soldiers to go back home as soon as possible. . . . But if those arrangements are not made, then we shall be responsible for the life and security of our people.

"If it the demilitarized zone is made sure, we'll come back withdraw . If it is not made sure, we'll stay there. Pressure won't help. We gave too much blood. We need to make sure it won't be necessary to do it again in a few years.

"If anybody tries to use pressure, I would like to tell you how Israel will behave," Begin told a cheering audience of representatives of American-Jewish organizations.

"Israel is going to behave as the Czechs should have behaved and didn't in 1938. So Israel will save the world and the world's peace."

He used the Czechoslovakia analogy again in another speech tonight before a dinner meeting of the United Jewish Appeal. On that occasion, he added:

"I would suggest to anybody who might think of using pressure, friendly or otherwise, on Israel not to try. We are not going to succumb to it."

Referring to an accident he had last winter, Begin said: "I broke a leg. But my knee is unbent."

The prime minister's emotional attempt to defend Israel's invasion of Lebanon by drawing a parallel with Nazi Germany's takeover of Czechoslovakia was a clear sign that he intends to present Israel's demands in tough and uncompromising terms when he discusses ways of resolving the Lebanon crisis with Reagan and senior administration officials.

His words were intended as a reminder to the world of how the major European democratic powers set the stage for World War II in 1938 by abandoning Czechoslovakia and forcing it to bow to Adolf Hitler.

Begin is scheduled to meet here Friday with Secretary of State Alexander M. Haig Jr., and he then will go to Washington for talks with Reagan on Monday.

Earlier this week, U.S. officials described the Monday session in tentative language as "scheduled, as of now"--a move intended as a warning of U.S. concern that Israel will go beyond its originally announced goals in Lebanon and seek to capture Beirut.

U.S. officials said they had been reassured by Israel that it will not seize Beirut, and Begin said today that "I will go on Sunday to Washington and I will meet with the president. . . ."

White House deputy press secretary Larry Speakes, speaking aboard Air Force One tonight as Reagan returned to Washington from New York, reiterated that the meeting with Begin is scheduled for Monday.

In his talks with Reagan and Haig, Begin is expected to press the Israeli view that the best way to establish and effectively police a demilitarized zone would be through creation of a multinational peacekeeping force containing American troops and operating independently of U.N. control.

The United States, after its initial anger at the Israeli invasion, has come around to the view that a "new reality" has been created that will allow resolution of the border tensions through setting up a demilitarized zone, helping the Lebanese government reassert control over the country's many feuding factions and bringing about the withdrawal of Syrian as well as Israeli troops.

However, the administration, aware that the idea of U.S. participation in the peacekeeping force would draw heavy opposition from Congress, would prefer to restructure and strengthen the U.N. force, known as UNIFIL, now in Lebanon.

Israel is mistrustful of UNIFIL, but the administration is working on plans for changing its mandate and mission in ways that might satisfy Israeli objections. The topic is likely to undergo high-level discussion when Begin and Haig confer.

In his speech this afternoon, Begin made a caustic reference to Chairman Charles H. Percy (R-Ill.) of the Senate Foreign Relations Committee, who has warned that Israel's failure to withdraw immediately could damage congressional support for the military assistance Israel gets from the United States.

Begin said, "Israel decided to put an end to the Palestinian outrage and show to the world we can keep the peace, that our children can go to school exactly as the children of Sen. Percy in Chicago."

In addition to reinforcing support within the American Jewish community, the prime minister also is seeking wider backing within the United States. Today, he called the president of the Southern Baptist convention, which is meeting in New Orleans, and urged him not to forget "the land the Jews have rebuilt."

The last president of the convention, the Rev. Bailey Smith, provoked criticism last year for remarks regarded as anti-Semitic. But other conservative Christian leaders such as the Rev. Jerry Falwell, head of the Moral Majority, have developed close relationships with Begin and have sought to use their influence on behalf of the Jewish state.