Nearly one-quarter of the American people may have an unfavorable opinion of First Lady Nancy Reagan, according to the latest Washington Post-ABC News Poll.

The poll asked this question: Do you have a favorable or unfavorable impression of Nancy Reagan? Of the 1,516 persons interviewed, 51 percent said they have a favorable impression of the first lady, 23 percent said their impression of her is unfavorable and the remaining 26 percent did not voice an opinion.

These findings come from interviews conducted from Nov. 17 to Nov. 22. The results are roughly similar to those of an October Washington Post-ABC News Poll. The current poll shows that a substantially larger percentage of Americans disapprove of Nancy Reagan than they did of Rosalynn Carter and Pat Nixon early in their husbands' administrations.

The first lady's press secretary, Sheila Tate, said that it was unfair to compare Mrs. Reagan with past first ladies. "Comparing her to Pat Nixon 10 years ago is like comparing apples to oranges," Tate said, adding that she thought Mrs. Reagan was not doing badly in the poll. "I'd be happy if that many people liked me."

Tate said yesterday that she feels Mrs. Reagan does not have an image problem. "She's just being herself," said Tate. "It's probably the hardest thing to do, given the pressures, but it's also the best."

In a recent press conference, President Reagan made it a point to say that his wife is getting "a bum rap" on the acquisition of new White House china funded by a private donor.

In recent weeks, Nancy Reagan's schedule has put her out front more, underscoring substantive activities, including her visits to drug rehabilitation centers and a meeting with a national parents group concerned about drug abuse. The poll was taken to determine whether, as a result of the first lady's schedule, her public image has improved over the last month.

The Gallup organization found 18 percent with an unfavorable rating of Nancy Reagan in a June 1981 poll, a figure higher than the 8 percent who expressed disapproval of Pat Nixon in March 1969 and the 7 percent who voiced disapproval of Rosalynn Carter in May 1977.

Criticism of Nancy Reagan in the November Washington Post-ABC News poll appears to be sharpest among blacks, lower income people and Democrats, while whites say they have a favorable impression of her by a 55-to-22 percent margin. Of blacks questioned, 35 percent say they have an unfavorable impression; 32 percent voiced their approval.

These are the same groups that previous polls have indicated are most likely to disapprove of the president. In part, Nancy Reagan's unfavorable impressions with these people could be a reflection of their critical views of her husband.

Tate said Mrs. Reagan's longstanding commitment to the underprivileged, many of whom are blacks and lower income people, includes her efforts on behalf of Foster Grandparents and in the area of drug and alcohol abuse among youth.

"She wants to get on with what she's interested in doing," said Tate. "There is nothing else she can do."