President Reagan last night called for a futuristic research and development effort aimed at providing a space or ground-based defense against Soviet intercontinental ballistic missiles by the end of the century.

A senior administration official said that the proposal, which was designed to dramatize the president's call for nuclear arms reductions, would take "decades to reach fruition," but Reagan described it as "an effort which holds the promise of changing the course of human history."

"We seek neither military superiority nor political advantage," Reagan said. "Our only purpose--one all people share--is to search for ways to reduce the danger of nuclear war."

The president did not discuss any specific arms reduction proposals in his nationally televised speech, which was devoted mostly to the theme that the Soviets were building "an offensive military force" that could be used to attack the United States or its European allies.

But Reagan said that he would give his views on this issue on March 31, when he is expected in a Los Angeles speech to propose an interim plan for reducing but not immediately eliminating intermediate-range nuclear weapons in Europe.

Last night, the president sought to build political pressure on Congress to approve the administration's proposed increases in the military budget. Reagan urged his viewers to tell their members of Congress that defense budget cuts "will send a signal of decline, of lessened will, to friends and adversaries alike."

Democratic reaction to the message was critical. House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) and Senate Minority Leader Robert C. Byrd (D-W.Va.) said the speech was directed to the defense budget, not national security, and asked the networks to give rebuttal time.

Sen. Edward M. Kennedy (D-Mass.) characterized the speech as "misleading Red-scare tactics and reckless Star Wars schemes." Two senators who are declared Democratic presidential candidates, Alan Cranston of California and Gary Hart of Colorado, also issued critical statements.

Reagan warned in the speech that "the Soviets have built up a massive arsenal of new strategic nuclear weapons--weapons that can strike directly at the United States."

He also contended that the Soviets have extended their power to the Western Hemisphere with installations in Cuba and the Caribbean island nation of Grenada and with military aid to Nicaragua.

"They are spreading their military influence in ways that can directly challenge our vital interests and those of our allies," the president said.

Administration officials acknowledged that the president's speech was timed carefully to coincide with the congressional debate on his defense budget and the upcoming Easter recess, during which members of Congress will test the reaction of constituents. The speech was cast to focus not on the increases in military spending that Reagan is requesting but on the nature of the Soviet threat.

Reagan illustrated his talk with graphs showing the dimensions of the Soviet buildup and with aerial photographs--some of them classified until early in the week--which purported to show Soviet fighter planes and intelligence headquarters in Cuba, Soviet weaponry in Nicaragua and a new airplane runway in Grenada. The Nicaragua photo had been made public previously.

An administration official said that the televised speech, which has been under discussion in the White House for several weeks, was an attempt by the president to "regain the political offensive" on the defense issue.

Polls taken for the administration show a steady decline of public support for the president's defense stand, with a majority of Americans favoring reductions in the military budget.

In a White House briefing before the president's speech, administration officials were vague on the details of Reagan's call for "a comprehensive and intensive effort to define a long-term research and development program to begin to achieve our ultimate goal of eliminating the threat posed by strategic nuclear missiles."

About $1 billion is currently being spent on such efforts by the United States, officials said, and even greater amounts by the Soviet Union.

Officials said that if scientists respond to the president's call they would expect to propose budget increases within the current fiscal year, but gave no estimates on the degree of any stepped-up effort.

They said that the expenditures would be consistent with the anti-ballistic missile (ABM) treaty with the Soviets, which expressly permits spending for research and development. The officials dismissed questions that such defensive measures might be destabilizing because they would encourage a superpower to launch a first nuclear strike, believing they could stop the other side's missiles.

But in his speech, Reagan expressed generalized concern about the problems associated with an ABM system.

"I clearly recognize that defensive systems have limitations and raise certain problems and ambiguities," Reagan said. "If paired with offensive systems, they can be viewed as fostering an aggressive policy and no one wants that."

Last night's speech was carefully orchestrated by White House officials, who have become sensitive both about news leaks and about prior lack of coordination in administration efforts to present the military budget in a positive light.

On Tuesday, network correspondents were informed that there would be "significant news" in the speech last night, news that was deliberately kept both from communications director David R. Gergen and White House spokesman Larry Speakes.

Yesterday, Reagan's call for the research and development on ABM was then carefully leaked to some of the same correspondents in an effort to get some, but not all, of the story told on the evening newscasts.

The White House also invited various dignitaries, including prominent nuclear scientists, for dinner in the State Dining Room. But the most prominent invited guest, Henry A. Kissinger, did not come, nor did the two secretaries of state in the Carter administration, Cyrus R. Vance and Edmund S. Muskie.