President Reagan redefined his position on limited nuclear warfare in Europe today in an effort to ease European allies' fears and counter Soviet charges.

Reagan, who last Friday said he could envision a nuclear war in Europe that neither superpower would escalate to a total nuclear exchange, today called that position unreasonable.

"The suggestion that the U.S. could even consider fighting a nuclear war at Europe's expense is an outright deception," Reagan said, explaining his Friday statement that "I could see where you could have exchange of tactical weapons against troops in the field without it bringing either one of the major powers to pushing the button."'

"The essence of U.S. nuclear strategy is that no aggressor should believe that the use of nuclear weapons in Europe could reasonably be limited to Europe," Reagan said today.

In Bonn, West German Chancellor Helmut Schmidt today issued a statement backing the president's remarks of last Friday, saying they represented "no departure from Western alliance strategy."

Although the president's statement today does not totally renounce the doctrine that a nuclear war is fightable and winnable, it is the furthest Reagan or any of his senior advisers has gone in that direction. Earlier, when Reagan and Defense Secretary Caspar W. Weinberger were asked about limited nuclear war, they declined to say whether they believed such a war is possible, but said the Soviet Union clearly thinks limited nuclear war is a possibility.

Reagan's Friday remark touched off political shockwaves in Europe where a growing anti-war, anti-nuclear movement alleges that Europe is being prepared to be a nuclear battlefield for the superpowers.

The Europeans have focused their concern on allegations that the United States is building up for such a limited war with the new medium-range nuclear missiles it wants to base in Europe.

The Soviet Union has been fanning such speculation and Soviet leader Leonid Brezhnev was quick to respond to Reagan's Friday remark. Brezhnev called any nuclear war "dangerous madness" that would lead to "suicide" for both superpowers.

The Reagan administration, clearly eager to take the rhetorical play away from Moscow, issued the statement today to reporters on Air Force One traveling with the president to Cancun for a summit on international development. It was also distributed in Washington and Cancun.

A distinction between Reagan's Friday remarks and his statement today is that the Friday remark was made off-the-cuff in a meeting with newspaper editors, while the new statement was issued in writing and clearly had been carefully drafted.

"In the past few days, the Soviet Union has issued several propaganda statements that seek to drive a wedge between the United States and some of our closest friends in Europe. I do not intend to let those gross distortions of our policies go unchallenged," the statement begins. The rest of the statement reads in full:

"American policy toward deterring conflict in Europe has not changed for over 20 years. Our strategy remains, as it has been, one of flexible response, maintaining an assured military capability to deter the use of force -- conventional or nuclear -- by the Warsaw Pact at the lowest possible level.

"As all presidents have acknowledged, any use of nuclear weapons would have the most profound consequences. In a nuclear war, all mankind would lose. Indeed, the awful and incalculable risks associated with any use of nuclear weapons themselves serve to deter their use.

"The suggestion that the U.S. could even consider fighting a nuclear war at Europe's expense is an outright deception. The essence of U.S. nuclear strategy is that no aggressors should believe that the use of nuclear weapons in Europe could reasonably be limited to Europe. Indeed it is the joint European-American commitment to share the burden of our common defense which assures the peace. Thus, we regard any military threat to Europe as a threat to the U.S. itself. Three hundred seventy-five thousand U.S. servicemen provide the living guarantee of this unshakable U.S. commitment to the peace and security of Europe."

Secretary of State Alexander M. Haig Jr. put a somewhat different emphasis on the question of limited nuclear warfare when he was asked questions here. Haig stressed that it has been NATO policy for 20 years to try "to maintain and terminate any conventional or nuclear conflict at the lowest level of violence."

From Bonn, Washington Post correspondent Bradley Graham filed the following report:

In a further effort to quell the furor here over remarks last Friday by President Reagan about a limited nuclear war, West German Chancellor Helmut Schmidt today formally backed the president's comments, saying they represented no departure from Western alliance strategy.

"The strategy of the North Atlantic alliance, unchanged for 30 years, has been the deterrence of attack against Western Europe by threatening to use all suitable military means," Schmidt said in a statement. "This deterrence strategy should never have been, and in the future should never be, misunderstood as preparing for waging a war in Europe.

"President Reagan has neither put in doubt nor veered from this valid deterrence strategy. The president has also not called any detail of it into question."

The German leader's statement was read to reporters following a regular West German government Cabinet meeting at which, according to a Bonn spokesman, Reagan's comments were the main topic on the agenda.

Speaking to the Bonn Cabinet, Schmidt attributed the excited reaction to "possible misunderstandings" or "mistaken interpretations" of Reagan's statements, according to a spokesman.