Secretary of State George P. Shultz, in an uncharacteristically long and emotional speech, suggested yesterday that self-limitation of U.S. power, such as voted by the House this week, could doom Central America to a fate similar to that which has befallen Indochina in the 10 years since the communist victory there.

The ostensible purpose of Shultz's 35-minute address to several thousand State Department employes was to commemorate the 10th anniversary of the fall of Saigon, which he described as a costly and needless failure of American power and self-confidence.

Smarting from a series of defeats on the House floor, Shultz used the occasion for a harsh attack-by-analogy on those who fought successfully against Central Intelligence Agency and other U.S. aid to antigovernment rebels in Nicaragua.

The American people "are tired of setbacks, especially those that result from restraints we impose on ourselves," Shultz said. He attacked what he said is a growing "litany of apology for communists and condemnation for America and our friends."

Addressing "head-on" the analogy between Vietnam and Central America that has permeated much domestic debate on the administration's program, Shultz compared the abuses of "Vietnamese communists" to those of "Nicaraguan communists."

"Broken promises. Communist dictatorship. Refugees. Widened Soviet influence, this time near our very borders. Here is your parallel between Vietnam and Central America," Shultz said.

The 15,000 anti-Sandinista guerrillas or "contras" whose CIA backing has been ended by Congress "deserve our support" and "are struggling to prevent the consolidation and expansion of communist power on our doorstep, and to save the people of Nicaragua from the fate of the people of Cuba, of South Vietnam, Cambodia and Laos," according to Shultz.

In his most explicit attack on the opponents of the contra aid, Shultz said: "Those who assure us that these dire consequences are not in prospect are some of those who assured us of the same in Indochina before 1975."

The often-impassive secretary of state is said by associates to have discussed the speech at length with President Reagan in advance and to have added much of his own thought and emotion to the document. Both Shultz's passionate anticommunism and his deepening frustration with congressional restraints on executive power were much in evidence.

"This was the real George Shultz talking," said an aide shortly after the address in the crowded diplomatic lobby of the State Department. Department employes, some of whom seemed startled by Shultz's intensity, did not interrupt with applause during the address and gave a warm but not notably enthusiastic ovation at the end.

A U.S. Marine in World War II, Shultz had little to do with the Vietnam war. He was a professor and dean at the University of Chicago from 1957 to 1968, the years of creeping U.S. involvement and military escalation, and served as labor secretary, budget director and treasury secretary as the war wound down during the Nixon administration. Shultz left Washington for private industry about a year before the fall of Saigon.

In a lengthy opening section, Shultz portrayed in some detail "the bloodshed and misery" arising from communist rule in Indochina, which he said has "fulfilled the worst predictions of the time."

Speaking of "the moral issue" in Vietnam, he repeated with approval Reagan's controversial 1980 campaign statement that the Vietnam war was "a noble cause." Evidently referring to the "horror" of the post-1975 events in Indochina, Shultz said, "Whatever mistakes in how the war was fought, whatever one's view of the strategic rationale for our intervention, the morality of our effort must now be clear."

Turning to the strategic price for the United States, Shultz said "the cost of failure was high." In addition to a setback in the global balance of military power, he said, the United States for a time "retreated into introspection, self-doubt and hesitancy."

"American weakness turned out to be the most destabilizing factor on the global scene," said Shultz, referring to a series of Soviet advances in Africa, the Mideast and Afghanistan.

Shultz devoted a major section of his address to comparing Vietnamese communist policies to those of the Nicaraguan governing authorities, whom he referred to repeatedly as communists. At the same time, he said that "the critical issue today is whether the Nicaraguan communists will take up in good faith the call of the [Roman Catholic] church and of the democratic opposition for a cease-fire and national dialogue" as proposed by Reagan April 4.