In the late summer and early fall of this year, the Reagan administration carried on a secret dialogue with the revolutionary government of Nicaragua in a concerted attempt, apparently unsuccessful, to head off an approaching collision of the two regimes.

The dialogue, which began in August and ended with an Oct. 31 Nicaraguan message, included more wide-ranging U.S. proposals than have previously surfaced in fragmentary accounts of the accommodation effort.

In diplomatic letters to Managua on Sept. 8 and Sept. 16, the United States presented drafts of statements pledging to "vigorously enforce" neutrality laws and clamp down on paramilitary exiles training on U.S. soil, and stating a commitment not to use or threaten force, as a matter of principle, against the Nicaraguan government. Washington also promised but never sent similar documents establishing the basis for resumption of cultural exchanges and U.S. economic and technical assistance.

In return, the United States insisted that Nicaragua bring a halt to the use of its territory for support of guerrillas in El Salvador and other neighboring states of Central America, a demand that was called the "sine qua non of a normal relationship."

In a draft document informally shown to a Nicaraguan official but never formally dispatched, Washington also proposed that Nicaragua's regular military forces be limited immediately to 15,000 to 17,000 men, which was the number Nicaragua acknowledged but was far short of the 23,000 or so in U.S. intelligence estimates.

The United States also asked in the draft that the Nicaraguan forces eventually be brought down to "traditional size" as existed under the Somozas, about 8,000 according to U.S. estimate. And the draft called for Managua to cease importing heavy weapons from Cuba and the Soviet Union and to agree to permit an international body, perhaps a unit of the Organization of American States, to play a part in verifying its arms commitments.

The security proposal, which clearly was among the foremost aims of the American administration, was considered unacceptable and out of the question by Nicaraguan officials who were aware of it. This is because the Sandinista revolution aimed from the first, almost above all else, to end U.S. influence over Nicaragua's domestic affairs.

Why the negotiations bogged down after what seemed to be a promising start--including the private declaration of Nicaraguan junta leader Daniel Ortega to Assistant Secretary of State Thomas O. Enders on Aug. 12 that "our efforts must not fail"--is a matter of dispute between the leaderships of the two nations.

In the U.S. view, the chances for a negotiated rapprochement were always uncertain but worth a try considering the grave dangers and high costs of the collision course the two nations seem to be on. The negotiating effort, in the Washington perspective, probably fell prey to internal collisions within the ruling group, and those taking the most strident and radical course won.

From the Nicaraguan viewpoint, Washington was offering less than had been advertised in its two initial draft papers, and asking too much in its explicit demands for an end to support of other revolutionary parties and limits on the military buildup.

In addition, Managua argued that a Reagan administration decision to cancel $7 million in aid arranged by the Carter administration, and to do so at a crucial moment in the dialogue, was inconsistent with the spirit of the conversations. And the Nicaraguans objected vociferously to several U.S. military exercises in Central America that took place while the negotiations hung in the balance.

Given the antipathy between a revolutionary leftist regime in Central America and what is in some respects a revolutionary rightist regime in Washington, perhaps the remarkable thing is that the dialogue took place at all. It was undertaken in Washington only after an internal argument with those who hew to the letter of the 1980 Republican National Platform declaration that "deplores the Marxist Sandinista takeover of Nicaragua," and opposed the Carter adminstration's aid program for the new regime. Evidently because of the sensitivity at home, the Nicaraguans were asked to keep the discussions with Washington strictly confidential.

According to a well-placed Latin diplomatic observer, at stake in the negotiations was whether the Sandinistas in power turn out to be Marxist-Leninists with heavy Soviet connections, or merely Marxists of an independent stripe, and whether Nicaragua is a revolutionary state waging war on United States policies, or a revolutionary state living within the limits of Washington's tolerance.

The public rhetoric and private comments of administration officials leave no doubt of their belief that, as of today, the Nicaraguans are proceeding down a road of "totalitarianism" and "militarization" on the Cuban model. Officials also charge that "Cubanization is moving very fast," saying that the number of Cuban military and security advisers is reported to U.S. intelligence to have risen from 500 to 800 at the start of the dialogue last summer to an estimated 1,500 to 2,000 today.

Secretary of State Alexander M. Haig Jr. and other senior officials have said at various times in recent weeks that Nicaragua "rejected" U.S. offers of accommodation; these were not described in detail. At the same time, Haig has been careful not to take the responsibility for foreclosing future prospects.

Speaking to the General Assembly of the OAS last week at St. Lucia, Haig declared, "If Nicaragua addresses our concerns about interventionism and militarization, we are prepared to address their concerns. We do not close the door to the search for proper relations."

Foreign Minister Miguel D'Escoto, whom Haig met in a 90-minute private session at St. Lucia, argued that "we didn't reject" the accommodation, and sought to pin responsibility on Washington for not answering the last written communication from Managua Oct. 31.

Junta leader Ortega, speaking to the State Legislative Council last Saturday, declared, "We left the door open to understanding with the United States," but went on to say, "We do not accept the door that the Americans are opening for us because it is too small that in order to pass through it, we would have to do it on our knees and we are not going to do that." The last statement drew applause from his political associates.

The dialogue began in a visit to Managua in mid-August by Enders, who as chief of the bureau of inter-American affairs is the State Department's leading figure on Latin American policy. In six meetings with Nicaraguan governmental and political leaders, Enders set forth U.S. concerns in blunt fashion, according to participants on both sides.

According to a Nicaraguan source, Enders said, "There is a fork in the road. One way leads to accommodation, the other to separation. We are afraid you may be too far advanced on the wrong road." But at the same time, he proposed and the Managua leaders agreed to explore a rapprochement based on mutual interests, sources said.

After Enders' return to Washington, the administration decided to take the initiative by drafting a series of proposals that could bring about a meeting of minds. On Aug. 31, Enders communicated with Ortega through the U.S. Embassy in Managua, reiterating that "the continued use of Nicaraguan territory to support and funnel arms to insurgent movements in the area would pose an insurmountable barrier to the development of normal relations."

Within this context, he said, the United States would begin exploring a rapprochement by passing through diplomatic channels a series of "illustrative drafts" of statements prepared in Washington.

On Sept. 8 the first of these drafts was presented to Ortega, along with a new letter from Enders promising four additional texts, on non-intervention in internal affairs; human and cultural exchanges; technical and economic assistance, and what was blandly called "a security proposal."

The Sept. 8 draft was of a unilateral statement to be issued by the State Department, assuming that agreement was reached on other issues. The eight-paragraph draft listed U.S. neutrality laws which would apply to Nicaraguan exiles and concluded that "the United States will vigorously enforce its laws in this regard."

In Managua the statement was a disappointment bordering on a dud. From the Sandinista point of view, the United States was merely promising to do what it should be doing already--enforce its laws to stop the paramilitary training of exile groups openly preparing to "oust the communists" from Nicaragua. Earlier in the year, Managua had complained about the exiles, and received a cable from Haig citing some of the same U.S. laws. But nothing was done about the exiles.

Adding to the unhappiness in Managua, this initial U.S. draft was accompanied by diplomatic notice that $7 million of the $15 million remaining in the Carter aid program for Nicaragua was being cancelled. The aid had been suspended by the Reagan administration early in 1981 because of Nicaraguan support for Salvadoran rebels. According to State Department officials, it was necessary to go forward to cancellation of some of the aid in early September because of a need to apply the money elsewhere in the world before the end of the U.S. fiscal year.

On Sept. 16 came another draft from Enders to Ortega, this one a proposed joint statement to be issued by the two governments on their adherence to the principle of non-intervention and non-interference in the internal affairs of other nations. The possibility was held out that Daniel Ortega or his brother, Humberto Ortega, head of the armed forces, might make an official visit to Washington, at which time the statement could be issued.

The proposed statement, based on the Rio Treaty of hemispheric "reciprocal assistance," would have committed the United States not to use or threaten the use of force against Nicaragua, and not to acquiesce in terrorist or armed acts from its soil aimed at Nicaragua. It would also have applied to Nicaragua in relations with its neighbors in Central America.

The idea of the statement was to address Sandinista fears about U.S. action to snuff out the Nicaraguan revolution. In the talks with Enders and other conversations, the Sandinista leadership insisted that its military buildup was necessary to defend against the U.S. threat.

Enders argued, according to U.S. sources, that the buildup would not be effective against the United States, which has a population 100 times Nicaragua's, and would only alarm Nicaragua's neighbors. Therefore, according to Enders, a pledge of U.S. non-interference might ease Managua's fears and make the military buildup unnecessary.

The first Nicaraguan response to all this was a Sept. 19 message to Haig from Foreign Minister D'Escoto complaining of forthcoming U.S. military exercises in Central America. In the U.S. view these were small-scale maneuvers of a normal nature, one of which involved one Navy tugboat, three patrol boats and two observation planes. In the Nicaraguan view the maneuvers in the midst of the discussions "seriously affected" the negotiations.

Enders responded on Sept. 28 expressing the U.S. view of the maneuvers and offering to permit Nicaragua to send observers. The assistant secretary of state also asked for additional reactions to the two drafts which had been presented, and suggested that he return to Nicaragua to carry on the negotiations in late October.

In the meantime, however, the situation between the two nations was deteriorating.

The American Embassy sometime in September had obtained the text of a speech attributed to Humberto Ortega, who had emerged as the leader of the most militant faction of the leadership, in which he reportedly declared, "Sandinism without Marxism-Leninism cannot be revolutionary."

Daniel Ortega, in an address to the United Nations General Assembly Oct. 7, excoriated the United States for its past and present behavior in Nicaragua and Central America. In the U.S. view, this abrogated an understanding that both sides would refrain from verbal attacks during the negotiations.

The internal political situation in Nicaragua took a turn with the ban on strikes, new action against the independent newspaper La Prensa, and the arrest of several leading businessmen for criticism of government policy.

Particularly important, in Washington's view, were intelligence reports that aid to the Salvadoran rebels continued through Nicaraguan territory. State Department officials now say they believe the flow of arms was shut down for about three weeks last spring, but continued the rest of the year. The arms influx to Salvador did not reach the earlier level, however, according to the State Department.

Some Nicaraguan officials, including Foreign Minister D'Escoto, denied that a flow of arms to Salvadoran rebels was taking place with the knowledge or acquiescence of the Sandinista regime. But Bayardo Arce, one of the foreign political chiefs of the Saninista movement, reportedly told an American diplomat in Managua that "we will never give up supporting our brothers in El Savador."

On Oct. 31, in response to U.S. prodding, Nicaragua sent its final written communication in the series to Enders under the signature of Victor Tinoco, vice minister of foreign affairs. Tinoco compained about all the matters which Managua had brought up before--the military exercises, the cancellation of aid, the absence of concrete action against Nicaraguan exile groups.

Tinoco added a few new complaints: about a "lie" by the American columnists, Rowland Evans and Robert Novak, claiming that 600 Cuban soldiers had arrived in Nicaragua, and about U.S. opposition to a Nicaraguan plan for negotiations involving guerrilla forces and the governing junta in El Salvador.

Summing up, the Nicaraguan said further consideration of the U.S. proposals would depend on U.S. actions regarding the exile training camps in Florida and "above all the relaxation of tensions that your government generates wih concrete acts in the area of Central American and the Caribbean."

He went on to say that Nicaragua hoped for realistic U.S. proposals, and wished to continue the dialogue.

The Oct. 31 response was read in Washington, but not in Managua, as a rejection of the negotiations to date. Haig and other high officials began speaking out more openly and angrily about the Sandinista regime shortly thereafter, and refusing to rule out military action to stop that country from proceeding down the road to menace North America's back door.