Two years ago, Ethiopian security police abducted and tortured a Central Intelligence Agency officer involved in a CIA covert propaganda campaign against the Marxist government in Addis Ababa, according to informed sources.

The officer was held captive for more than a month, suffering a fractured skull, chipped vertebrae and dislocated shoulders during his captivity. He was freed in February 1984 when then ambassador-at-large Vernon A. Walters flew secretly to Addis Ababa, confronted Ethiopian leader Mengistu Haile-Mariam and obtained the officer's release, the sources said.

According to these sources, the CIA officer was subjected to hours of terror, including a form of "Russian roulette" played by his captors, and was denied sleep for five days until he signed a confession stating he worked for the CIA. He was constantly bound during this period and was not allowed to shower for 35 days.

The administration never publicly protested the incident, which U.S. intelligence officials say is one of the worst attacks by a foreign government on a CIA officer working as an accredited diplomat. But accounts of the episode have circulated in the administration and Congress, contributing to the general deterioration of U.S. relations with Ethiopia.

Since 1981, the CIA -- under authorization by President Reagan -- has provided about $500,000 a year to support propaganda and resistance tactics by an anticommunist group of Ethiopian dissidents, according to informed sources. In recent months, senior administration officials have begun preliminary planning for covert paramilitary training of armed guerrillas committed to overthrowing the current Ethiopian regime, the sources added, although no decision has been made by the White House on whether to provide munitions or other lethal aid.

Since last fall, senior Reagan administration officials have escalated their rhetoric against the "Soviet-style" government imposed by Mengistu and his military colleagues on a nation that once was among America's closest allies in Africa.

In public statements, Reagan and Secretary of State George P. Shultz have begun including Ethiopian "freedom fighters" among the Third World's anticommunist guerrilla movements deemed worthy of U.S. support as part of what conservatives call the "Reagan Doctrine," a concerted effort to roll back Soviet gains in the Third World.

Conservatives in and outside the administration are pressing for an extension of that doctrine to Ethiopia, which for nine years has had strong backing from the Soviet Union and Cuba and now is realigning Ethiopian government and society along classic East bloc lines.

The tortured CIA officer was working in Addis Ababa under diplomatic cover as a commercial attache in the U.S. Embassy, where he was deeply involved with small antigovernment resistance cells, sources said. The Washington Post chose not to publish the officer's name in this article because of concern about the safety of his associates.

The officer and other CIA employes in Addis Ababa directed a covert propaganda campaign intended to stir up discontent with Mengistu's regime. The CIA hoped to build an anticommunist opposition that eventually could attract broad political support and field an armed guerrilla force, the sources said.

In the weeks after he disappeared on Dec. 20, 1983, U.S. officials did not know who had seized the CIA officer or where he was being held. A worldwide alert was issued to all CIA stations in a frantic search for the missing officer, sources said.

The Walters mission to Addis Ababa was mounted after Israeli intelligence officials informed the CIA that the missing officer was being held by Ethiopian security police at an undisclosed location in Ethiopia.

One source said that Walters threatened the Ethiopian leader to obtain the CIA officer's release during a meeting with Mengistu on Feb. 4, 1984. Walters said through a spokesman yesterday, "I have been involved in many discreet negotiations and I'm not going to comment on my role in any of them." As for his reported meeting with Mengistu, Walters said, "It is just not my style to threaten anyone."

Following the release, Ethiopia expelled three other Americans without explanation. These diplomats included the CIA station chief at the embassy, the deputy station chief and another CIA officer, all of whom were operating under diplomatic cover, sources said. The United States retaliated by expelling two Ethiopian diplomats here.

The kidnaped officer, who resides in the Washington area and who is said by sources to have been treated for "post-trauma syndrome" as a result of his captivity, was not available for comment yesterday. Some of the sources who discussed the case say they believe the United States should escalate its effort to topple the Marxist Ethiopian regime.

These sources also have criticized the CIA for what they contend is a reluctance to support stronger covert measures against the Mengistu's regime because of concern that CIA officers engaged in normal intelligence collection activities in the region might be jeopardized.

A CIA spokeswoman said she would neither confirm nor deny that one of the agency's officers had been kidnaped and tortured.

The current state of relations between the United States and Ethiopia, strategically located on the Horn of Africa, is an example of how the Reagan administration -- after five years of uneasy dialogue with a number of Marxist African states -- appears to be moving toward a more confrontational approach toward these regimes, with the CIA taking the lead role.

Last fall, Reagan approved a $15 million CIA covert paramilitary program to assist rebel forces fighting the Marxist regime in Angola. More recently, the administration decided to provide the guerrillas with sophisticated Stinger antiaircraft missiles.

Some conservative groups are calling on the administration to make a similar commitment to the anticommunist resistance in Mozambique.

According to informed sources, administration officials have engaged in preliminary discussions in recent months on how to escalate CIA support for Ethiopian dissident groups dedicated to overthrowing the Mengistu regime.

One Ethiopian exile leader has met with Reagan. This leader, Yonas Deressa, said in an interview that he has been told by sources close to the White House that his cause will receive priority attention after Congress disposes with the president's request for additional aid to the contras fighting the Nicaraguan government.

One difficulty for U.S. strategists has been trying to identify a resistance group with a reasonable chance of success that espouses neither Marxism nor secessionism, since the administration strongly opposes movements dedicated to fracturing Ethiopian territory.

One group, the Ethiopian People's Democratic Alliance (EPDA) based in London, has received covert CIA support since 1981, according to informed sources. But this group has few guerrillas in the field and scant popular support inside Ethiopia, according to U.S. sources.

Among the strongest dissident factions, the Eritrean People's Liberation Front has been fighting for years to split the northern province of Eritrea away from Ethiopia. The Tigrans, also a northern ethnic group, have their own liberation front which is partly Marxist.

In Congress, there also has been a hardening of attitudes toward the Ethiopian government parallel to that of the White House. Legislation with bipartisan support has been introduced in the House to declare Ethiopia a communist state and thus pave the way for the Reagan administration to impose economic sanctions against the Mengistu regime.

The U.S. Agency for International Development, which has provided hundreds of million of dollars in emergency relief over the past two years, is considering an end to this aid at the end of this year, according to AID sources. Senior AID officials, including Administrator M. Peter McPherson, are convinced that the Ethiopian government's agricultural policies -- particularly the forced resettlment of 600,000 peasants and the start-up of a nationwide program of Soviet-style collective farming -- are nowmore responsible than natural causes for food shortages and famine-related deaths.

Reagan, in 1981, signed a presidential "finding" under the National Security Act authorizing the CIA to conduct a "nonlethal" campaign to support the democratic resistance to Mengistu's regime, informed sources said. As a result, the CIA earmarked an initial $500,000 to help the EPDA conduct a small propaganda war against the Marxist government, a campaign hampered from the start by squabbling and divisions within the group.

The propaganda campaign included a CIA contract with a Washington consultant, who wrote antigovernment material criticizing Ethiopia's internal policies, according to informed sources. Such written material, along with audio and video tapes of anti-Mengistu speeches by leading exiles in the United States and Europe, have been shipped to Addis Ababa in diplomatic pouches, where it is given to dissident "cells" for distribution throughout the country.

The CIA rejected a $546,000 request from an EPDA splinter group, which in October 1982 presented the CIA with a plan for military training in the Sudan for 300 guerrilla leaders who would then infiltrate Ethiopia to organize a resistance movement.

The CIA, according to informed sources, limited itself to helping the EPDA produce and distribute antigovernment propaganda inside the country. The captured agent was caught inside the home of one EPDA member, where he was hiding inside a secret closet which was part of a storage area for such materials, sources said.

The capture led to the breakup of an EPDA network inside the capital and the arrest of 18 of its members, the sources added.

Despite five years of CIA involvement with this Ethiopian opposition group, the U.S. opposition to the Mengistu regime has remained comparatively low-level and has had little visible impact on the regime.

The Reagan administration's position toward the Mengistu government hardened last fall. In his speech before the United Nations Oct. 24, Reagan listed Ethiopia with Afghanistan, Cambodia, Angola and Nicaragua as the five countries whose Marxist governments had embraced "an ideology imposed from without" and were "at war with their own people."

On Nov. 13, Assistant Secretary of State Chester A. Crocker disclosed for the first time that Washington made several efforts, the latest starting in October 1984, to improve relations with the Mengistu regime and was rebuffed.

"Each, originally promising, ended in failure," he said in a speech. "The Ethiopian leadership, apparently fearful of its Soviet mentors, would not permit any real progress in this direction [toward better relations]."

Crocker's hard-hitting speech marked a turning point, administration officials said. It reflected the disillusionment throughout the administration toward the lack of response from the Mengistu government either to the massive U.S. emergency relief aid -- 432,000 tons of food worth $243 million in fiscal year 1985 -- or U.S. efforts to improve relations.

"At that point, people here said the hell with it. Let's put the pressure on," one administration official said.

Much of the pressure has come from Congress, where conservatives last summer tied an amendment to the 1985 foreign aid bill requiring Reagan to determine whether the Mengistu government was engaged in a "deliberate policy of starvation of its people" and denying fundmantal human rights to its people. If so, Congress would impose a trade embargo on Ethiopia.

The determination was a subject of a struggle within the administration, particularly between the State Department, which opposed imposing economic sanctions in principle, and AID, which was much more ready to take action, according to congressional sources.

The outcome was a compromise. The Sept. 9 determination described the Ethiopian human rights record as "deplorable" and said the government's "political, economic and military policies have no doubt caused vast and unnecessary human suffering, including starvation."

However, it also said the available evidence did not justify the conclusion the government was "at this time conducting a deliberate policy of starvation" and thus no trade embargo was urged.

In Congress, a bill sponsored by Rep. Toby Roth (R-Wis.) and amended by Rep. Stephen J. Solarz (D-N.Y.), would formally classify Ethiopia as "a communist country." The measure has been supported unanimously by the House Africa subcommittee. This determination would mean the loss of Export-Import Bank loans and favorable trade terms with the United States. The bill would also urge a trade embargo if the Marxist government continues its resettlement program.