It was incorrectly reported yesterday that the Reagan administration envisions spending about $25 million over the next four years on research on a defensive, anti-missile system in space. The correct figure is $25 billion.

President Reagan today defended his call for a "Star Wars" anti-missile system in space, arguing that the United States has a "moral obligation" to develop such technology. He also claimed that his administration had brought "new energy and moral purpose" to foreign policy that would eventually lead to nuclear arms reductions.

His remarks came as Vice President Bush, in a speech also aimed at the war-and-peace issue, said in Texas that Walter F. Mondale, not Reagan, is to blame for the breakdown in arms talks with the Soviets. Bush said the Democratic presidential nominee has pledged to eliminate such weapons systems as the B1 bomber and the MX missile and the Soviets are simply waiting to see if he is elected.

Reagan, in a speech to the American Legion convention here, also fired back at Mondale on the issue of religion and government. The president said he does not favor government establishing a religion in this country, but also opposes those who argue for "freedom against religion."

On the establishment of a defensive weapon that could stop an intercontinental ballistic missile in space, Reagan said, "We must pursue vigorous research on defensive technologies that can permit us to intercept strategic ballistic missiles -- fired deliberately or accidentally -- before they reach our own soil or that of our allies." Reagan said, "Some call this Star Wars; I call it prudent policy and common sense."

It was the first time that Reagan had spoken out for the "Star Wars" proposal in a major speech since he proposed the idea in a nationally televised address on March 23, 1983. Since then, his administration has increased the budget for research on a defensive missile by $250 million to a total of $1.17 billion in the 1985 fiscal year.

The Soviets have charged that this shows an intention by the Reagan administration to violate a 1972 treaty signed by both nations prohibiting an anti-ballistic missile defense. The administration says research is expressly permitted by the treaty.

Deputy Press Secretary Robert Sims said today that the administration envisions spending about $25 million in research on a defensive missile over the next four years.

Opponents of the project, some of whom contend that a defensive system would make nuclear war more likely and accelerate the arms race, include Mondale, who will address the Legion convention on Wednesday.

Reagan also used his speech today to assert that his approach to foreign affairs will pay dividends in the future.

"Even as we have successfully resisted Soviet expansionism, we have opened a wide series of diplomatic initiatives that will eventually bear fruit not just in arms control treaties, but in arms reduction treaties," Reagan said. His speech to the legionnaires' convention was repeatedly interrupted with applause.

Reagan gave no examples of diplomatic activity to buttress his claim that his policies will lead to agreements with the Soviet Union. During the Reagan administration, the Soviets have walked out of two sets of arms talks in Geneva.

The president sought again to defuse the religion issue, which Mondale continues to use in his attacks against Reagan.

Speaking at a prayer breakfast in Dallas during the Republican convention last month, Reagan said that "religion and politics are necessarily related." Mondale charged in a radio speech last Sunday that Reagan and his supporters "had raised doubts whether they respect the wall our founders placed between government and religion," and he contended that the mixing of politics and religion threatens to "corrupt our faith and divide our nation."

Reagan said today that this was a misreading both of his position and of the intention of the founders to simultaneously erect a constitutional wall between church and state while providing for the free exercise of religion.

"They knew that morality derives chiefly from religious faith and that government no more should handicap religious expression than it should show preference for one religious group over another," Reagan said. "I can't think of anyone who favors the government establishing a religion in this country; I know I don't. But what some would do is twist the concept of freedom of religion to mean freedom against religion."

Reagan misread a word of this statement on the teleprompter, saying "handle" instead of "handicap."

He went on to say that when he uses the words "church" and "religion" they are with a lower-case "c" and "r" and that religion is a value that must be protected in a pluralistic society.

"The unique thing about America is that every single American is free to choose and practice his or her religion, or to choose no religion at all," Reagan said. "And that right must not and should not be questioned or violated by the state."

The president concluded his comments on religion by asking for support in passing a constitutional amendment permitting prayer in public schools, which he has long advocated.

Arriving in Chicago later, Reagan told reporters that his remarks in Dallas had been "distorted," and added: "My concern is not with government invading religion; it's with all those people that are trying to turn around and make government interfere with people's right to prayer."

Here in Utah, 70 percent of the population belongs to the Church of Jesus Christ of Latter-day Saints, commonly known as the Mormons. The Mormons, who in the past sometimes were persecuted at government instigation, believe in separation of church and state.

Before his speech this morning, Reagan met with leaders of the Mormon hierarchy. Reagan has no political problems in Utah, which he won in 1980 with 73 percent of the vote. A current poll here gives Reagan 70 percent of the vote.

In his speech, Reagan also urged a simplified tax system, calling the present system "unfair, inequitable, counterproductive and all but incomprehensible -- even Albert Einstein had difficulty with his Form 1040."