In his nationally televised news conference last night President Reagan followed a carefully prepared strategy designed to take strong personal command of the forum and use it to drive home his message that the United States is not headed for a military quagmire in Central America.

As they prepared for the news conference in the White House family theater yesterday, presidential advisers said they anticipated that Reagan would be confronted by a barrage of questions about the scope and intensity of U.S. military activity in the strife-torn region.

To accomplish their goals in Reagan's handling of these questions, they said they wanted the president to stay on the rhetorical offensive for as long as possible, a task that has sometimes been difficult for him in the past.

At his last news conference earlier this month, Reagan was thrown on the defensive by repeated sharp questions about how his 1980 campaign received documents from inside the Carter White House. Reagan appeared ill-prepared and ill at ease during that session.

This time, Reagan set out to use his rhetoric and the structure of the news conference to his advantage. Following a plan, he broke with past practice in the order of questioning.

Traditionally, the two major wire services are recognized at the outset of the news conference, and then correspondents are selected at will. Last night, however, once the wire service questions were finished, Reagan recognized three new White House correspondents, at least one of whom was told in advance of the president's plan.

All three of these reporters focused their queries on the military situation in Central America, and Reagan kept up his insistence that he wants a "political and a peaceful solution" in the region.

It was during these questions that the president also reached back to his 1980 campaign debate with President Carter for a line that was intended then, as well as now, to defuse concern that he would recklessly lead the nation into war.

After asserting that "we're not planning a war and we don't think that's going to happen at all," Reagan declared:

"I've seen four wars in my lifetime. I have sons and I have a grandson and I agree with Gen. Eisenhower that war is man's greatest stupidity. And I don't want to see such a thing. We want peace."

Reagan's strategy last night also was set with the release of a letter to the heads of the four Latin nations in the "Contadora" group seeking a regional solution to fighting in El Salvador and Nicaragua. Reagan sought to align himself with their efforts, even though the Contadora group has set conditions different from his for a peace settlement in the region and some of its members have criticized as ill-timed the large-scale U.S. military maneuvers that are to begin next month in Central America.

The president also peppered his opening statement and answers last night with reassurances of his commitment to "peace," to "social justice," to "reform," to "an end to violence and bloodshed," and to "dialogue and negotiations."

He cast the planned military exercises in the region as part of a continuing pattern going back to 1965 and said larger exercises have taken place in Europe, Asia and Latin America. While exercises in the Mideast and NATO countries have involved more troops, Pentagon officials have said the planned Central America exercise is larger than any other conducted in the region.

The White House script last night did not fall perfectly into place. Reagan expressed ignorance about the extent of the military exercises he has approved.

He also seemed taken aback at a question about why no women were included on the National Bipartisan Commission on Central America headed by Henry A. Kissinger. Reagan appeared to fumble for an explanation, saying that "maybe" it was because he had appointed so many women that "we're no longer seeking a token or something."

He also claimed he had put six opponents and six supporters on the commission--an assertion that might surprise some White House officials who expect most of them to support Reagan's overall goals.