WASHINGTON (AP) _ Anti-abortion activists expressed disappointment Monday at Nancy Reagan's reported declaration that ''I don't give a damn about the right-to-lifers,'' but they praised President Reagan's steadfast support for their cause.

The first lady was quoted by former White House chief of staff Donald T. Regan in his new book, ''For the Record: From Wall Street to Washington.''

Regan wrote that during a telephone conversation from Washington with Mrs. Reagan at Camp David, Md., on Jan. 24, 1987, the first lady demanded that all mention of the abortion issue be eliminated from the draft text of her husband's State of the Union address.

''I pointed out that the president had particularly wanted some language on this subject included in his address,'' Regan said he responded.

He quoted Mrs. Reagan as saying: ''I don't give a damn about the right-to- lifers.''

The State of the Union speech that the president delivered three days later contained no references to abortions.

White House spokesman Marlin Fitzwater told reporters Monday that ''I don't have any knowledge at all'' whether Mrs. Reagan actually made such a statement.

Elaine Crispen, the first lady's press secretary, refused comment.

Anti-abortion leaders, asked for reaction, refrained from any direct criticism of Mrs. Reagan and chose instead to praise her husband for his unwavering support.

''If, in fact, Mrs. Reagan's quote is accurate, we are very disappointed, but it does not affect the respect we have for how the president has helped the pro-life movement throughout his administration,'' said Tom Glessner, executive director of the Christian Action Council, an evangelical Protestant organization.

''We would ask Mrs. Reagan to ... let us know if, in fact, this is how she regards the right-to-life movement,'' Glessner said.

Kay James, public affairs director for the National Right to Life Committee, the largest U.S. anti-abortion organization, refused to discuss the first lady or her remarks.

''I think what's important is what the president has done,'' she said. ''What is apparent to us is that the president has always been extremely supportive in all his speeches, his initiatives and his policies, and that's what we have to go on.''

Said Jack Fowler, Washington bureau chief of the Ad Hoc Committee for Life, an anti-abortion lobbying group: ''It's upsetting, if it is true, although it doesn't change our attitude toward the president himself. We know the president is pro-life.''