The American Civil Liberties Union has launched a major appeal to its members for help against what it calls a new menace to constitutional rights: nuclear power.

In an August mailing to its 170,000 members, the New York-based group said pressure for a solution to the energy crisis has already led to deception, secrecy, "monumental due process violations" and police surveillance of those who oppose nuclear energy.

"As unlikely as it may seem at first glance, the development of nuclear power holds profound and dangerous implications for civil liberties," the ACLU letter said.

Signed by ACLU executive director Ira Glasser, the letter noted "the 25-year cover-up surrounding the testing of nuclear weapons in Nevada and Utah," calling it "as serious an abuse of power as Watergate."

Glasser said in an interview that the letter was not meant to attack nuclear power itself. "It may be a little vague in some of its phrases, but we do not and will not get involved in the merits of nuclear energy one way or the other," he said. "I regret any implications in the letter to the contrary."

The nuclear power industry, however, was not convinced. "The whole letter is rather emotional and irresponsible," said George Gleason of the American Nuclear Energy Council, the industry's lobbying arm.

"The average person reading this is going to get the impression that the ACLU has evaluated the technology involved and found it wanting . . . they have rolled in what appears to be an ideological position with a totally separate civil rights issue."

The industry, Gleason said, disagrees with the letter's "misleading impression that the technology inherently requires inappropriate measures to control it . . . we don't think that is an extraordinary problem."

Glasser said he had received "a dozen or so" responses from members who are also worried about the antinuclear tone of the letter. "We're only interested in the fact that any issue that becomes a great political contest tends to be accompanied by violation of civil liberties," he said.

The letter cited the internment of Japanese-Americans during World War II, loyalty oaths required during the anticommunist heyday of Sen. Joseph McCarthy (R-Wis.) in the 1950s, and "secrecy and suppression surrounding Vietnam."

Noting court orders that prevented publication of an article on the hydrogen bomb in Progressive magazine, the letter said: "The Carter administration's secrecy mania . . . has proved to be even greater than the Nixon administration's in the Pentagon Papers case."

FBI agents have tried to discredit investigators in the case of Karen Silkwood, who was killed trying to expose alleged safety violations at an Oklahoma plutonium processing plant, the letter charged. The FBI, local police departments and power plants, it said, have put together dossiers on antinuclear demonstrators, tried to disrupt their gatherings and sought access to police intelligence records on them.

"These are but a few of the many examples which illustrate the lengths to which government and the nuclear power industry will go to harass, intimidate and silence critics," the letter said. "The issues surrounding nuclear energy are not easy issues. But, there can be no doubt that they are civil liberties issues," it continued.

Glasser stuck to that view. "Governments will always overreact to claims of national security," he said. "A protest begins and immediately the surveillance machine cranks up, citing vague links to communism when there's no evidence at all for it . . . it's beginning to happen again."

The Nuclear Regulatory Commission is now considering a set of proposed security clearance regulations for power plant employes that the ACLU letter called "a direct and immediate threat to First Amendment freedoms of speech, dissent and association." Gleason said such a danger ought to be considered but added he did not think the current proposals make up such a threat.

The ACLU asked its members for "special contributions" of $20 or more to "enable us to fight to secure the public's right to know and participate in the great energy debate." It quoted ACLU legislative director John Shattuck as saying in a recent speech, "I would prefer to read the Constitution by candlelight than not to read it at all."

Adoption of the nuclear issue marks a new phase in the life of the 59-year-old ACLU, which peaked at the end of the antiwar movement in 1974 with 275,000 members. About 30,000 members resigned last year in the wake of the ACLU's defense of the right of Nazis to march through Skokie, Ill., a Chicago suburb that is home for many survivors of Hitler's concentration camps.

Glasser said some had begun to rejoin and that recent recruitment drives had been successful. He took over last year, overseeing a staff of about 5,000 volunteer lawyers with offices and affiliates in 500 cities.