President Reagan yesterday singled out for human-rights abuses a dozen nations ranging from the Soviet Union to South Africa, while an administration spokesman said the Soviets were engaged in an "odious" attempt to present doctored television films falsely depicting dissident Andrei Sakharov as being in good health.

Signing an annual proclamation observing Human Rights Day, the president strongly condemned Soviet behavior in Afghanistan where he said that invading troops had "slaughtered innocent women and children" and used poison gas.

But Reagan also used some of the strongest language he has ever employed against the South African government and criticized the human-rights practices of such U.S. allies as Chile and the Philippines.

"In South Africa, the inhuman policy of apartheid continues," the president said. "The declaration of a state of emergency has given the police in that country essentially unlimited powers to silence critics of the government."

Reagan has given a human-rights speech every year during his presidency, but this was by far the most wide-ranging in the number of countries and abuses singled out for criticism. Administration officials said the speech was deliberately "global" in its approach and that Reagan, despite his description of Soviet behavior in Afghanistan, still believed that "quiet diplomacy" was the best way to resolve specific Soviet human-rights cases.

The president said he had "made it very clear" in "long and confidential" discussions with Soviet leader Mikhail Gorbachev at the Geneva summit "that human rights are an abiding concern of the American people."

"Make no mistake about it, human rights will continue to have a profound effect on the U.S.-Soviet relationship as a whole, because they are fundamental to our vision of an enduring peace," Reagan said.

Earlier in the day, White House spokesman Larry Speakes denounced Soviet "self-serving film clips," portions of which have appeared on television in the United States. The clips show Sakharov relaxing in the city of Gorki, to which he has been exiled, and carrying suitcases for his wife, Yelena Bonner, now in the United States for medical treatment. Administration officials said the film apparently was edited so that it could not be seen that Sakharov, weakened from a six-month hunger strike, could carry the suitcases only a few steps.

"The films are clearly designed to deflect attention from Soviet mistreatment of Dr. Sakharov," Speakes said. "They do not provide credible information about his state of health. We find particularly odious the Soviet practive of filming Dr. Sakharov and his wife Mrs. Bonner without their knowledge during medical examinations and consultations, in violation of basic medical ethics."

A new element of the president's human-rights speech this year was his denunciation of the "rampant religious persecution" in Iran of members of the Bahai faith, a religion which stresses universal brotherhood. Reagan said that the government of Iran had killed 198 Baha'is, imprisoned 767 and forced 35,000 others to flee their homes or their country.

In a ceremony in the Old Executive Office Building, the president also said that "the communist rulers of Vietnam have launched vicious attacks upon Cambodian refugees," and that "in Ethiopia, a Marxist government has used famine to punish large segments of its own population." He also criticized Cuba and the Sandinista government in Nicaragua.

"On three continents we see brave men and women risking their lives in anticommunist battles for freedom," Reagan said. "We cannot and will not turn our backs on them."

Reagan did not stop today, as he sometimes has in past speeches, with denouncing leftist regimes. He said South African apartheid was "abhorrent" and that "in Chile and the Philippines, we've shown our strong concern when our friends deviate from established democratic traditions." "Governments that must answer to their peoples do not launch wars of aggression," Reagan said. "That's why the American people cannot close their eyes to abuses of human rights and injustice, whether they occur among friend or adversary or even on our own shores."