A week of intense debate in Congress on American policy toward Nicaragua has raised the political temperature in Washington but has not altered the U.S. role in Central America.

This week's excitement in the House and Senate provided a lesson in the interplay of domestic politics and foreign policy, demonstrating again that in a showdown, both the policy-makers and the politicians worry as much about how a controversial policy proposal looks as about how practical it may be.

Republicans led by President Reagan sought to make the debate virtually a test of sentiment on communism, while Democrats led by House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) tried to paint aid to "contra" rebels fighting the Nicaraguan government as the first step toward a war like the one in Vietnam. Yesterday Secretary of State George P. Shultz restated the Vietnam analogy to suit administration purposes:

"Our goals in Central America are like those we had in Vietnam: democracy, economic progress and security against aggression," he said. "Broken promises. Communist dictatorship. Refugees. Widened Soviet influence, this time near our very borders. Here is your parallel between Vietnam and Central America."

It is significant for the future that most Democrats probably would agree with Shultz's goals for Central America, and many also would accept his description of the situation. Virtually no member of the House or Senate defended Nicaragua's leftist Sandinista government during the debate.

But, just as in Vietnam, the increasingly divisive question is what means the United States should use in Nicaragua to achieve the goals of democracy, peace and progress.

The week's five major congressional votes ended with no new policy decisions.

A Reagan letter full of policy promises that was instrumental in winning a victory for the White House in the Senate was nullified when the overall aid request failed to pass in the House. That restored a status quo that had been in effect since last October.

The last U.S. checks to some 15,000 armed contra insurgents fighting the leftist Sandinista government went out last May, and Congress refused this week to provide any more.

However, the new political heat over Central America may be pushing both sides toward a real compromise a few weeks down the road.

Republicans have warned repeatedly that only the insurgents stand between growing Soviet influence in Central America and the need to commit U.S. troops to stem the tide.

They assert that military pressure from the rebel "freedom fighters" has produced concessions from Nicaragua toward regional peace and that only more pressure can change the current government's policies.

But most congressional Democrats don't accept that analysis. Many who have given Reagan what he has wanted on other controversial issues such as the MX missile have drawn the line on Nicaragua.

They now have blocked further assistance to the insurgents five times since late 1982, arguing that no matter how repellent the policies and the practices of the Sandinista government, the United States has no business financing a guerrilla army to overthrow it by force.

Again and again in the debate, Democrats argued that the contras and their 3-year-old war were brutally immoral, illegal and counterproductive, serving only to reinforce the Sandinistas in their repressive behavior.

Yes, they said, use pressure on Nicaragua, but make it diplomatic, political, economic -- anything but military by proxy.

The White House, faced with a humiliating defeat, backed down.

Five days before the first Senate vote, the only one that Reagan won, he agreed to ask only for "nonlethal" aid, excluding only weapons and ammunition.

But that was not enough.

Following Capitol Hill conferences over the weekend, eight Senate Democrats joined by several Senate Republicans met Reagan and his senior aides in a highly unusual eight-hour conference at the White House Monday.

Nothing was resolved, but early Tuesday morning White House national security affairs adviser Robert C. McFarlane began drafting a presidental letter aimed at wavering Democrats to deal with some of their concerns.

An administration official familiar with the process said the degree of conciliation had to be weighed against the needed legislative support.

"If we adopt three of these Democratic proposals , do we win three Democratic votes? And how far can we go toward meeting Democratic concerns before we start losing the votes of our own conservatives," the official said.

Shultz took the lead in negotiating the text of the Reagan letter with wavering Democrats.

In mid-afternoon Tuesday, he showed the draft document to Sen. Sam Nunn (D-Ga.), who complained that it did not include U.S. economic sanctions against Nicaragua or any effort to halt human rights abuses by the rebels.

Less than an hour later, Nunn said, administration officials returned with two new paragraphs for the letter covering those issues.

The senator approved one on the spot and penciled in another half-sentence for the other paragraph.

Sen. Lloyd Bentsen (D-Tex.), another waverer, told Shultz that "a casual reference" to economic sanctions was not enough.

"It then became much more specific," Bentsen recalled. Would he have voted for more rebel aid without that paragraph? "I didn't have to face up to that. I got it," he said.

Several such paragraphs and meetings later, the letter was delivered and the Senate voted 53 to 46 to provide nonlethal aid to the rebels through the Central Intelligence Agency.

But the House rejected the compromise, with many members arguing that the letter was full of loopholes and did not really change much.

Asked by skeptical reporters if the letter is legally binding, Shultz said immediately after the Senate vote that "the president of the United States, Ronald Reagan, has made these statements to Sen. [ Robert J.] Dole and Sen. [Robert C.] Byrd and he will abide by them, no doubt about it."

But yesterday White House spokesman Larry Speakes said "the whole letter was conditional on passing legislation" to aid the contras.

Other officials said the letter was nullified by the final negative vote.