United States intervention in the civil war in El Salvador began with President Carter. In 1980, the last year of his administration, he sent in five US military advisers and $5.5 million in ''nonlethal'' military assistance. The main item on the list of ''nonlethal'' things was a pair of military transport helicopters.
This program was suspended on Dec. 5 after the disclosure on Dec. 2 of the slaying of three Roman Catholic nuns and a fourth Catholic lay worker. The suspension was lifted on Jan. 14, 1981, after an investigation of the slayings failed to produce evidence of complicity by government armed forces, and following reports of the shipment of arms to the El Salvador rebels from Nicaragua and Cuba.
On March 2, 1981, President Reagan approved a step-up in the amounts of US military aid. He added 20 more US military advisers and an additional $25 million in military aid. But he assured the Congress that no US troops would go into battle in El Salvador.
During the rest of 1981 the rebels continued to peck away at government units with increasing frequency and success. By December the Reagan aid on top of earlier Carter aid had not turned the tide of battle in the civil war. On Dec. 15 the White House announced a program for training Salvadorean troops and authorized another $18 million for the training program.
On Jan. 9, 1982, the first contingent of Salvadorean troops (60 men) arrived at Fort Bragg, N.C., for training by Green Beret instructors.
On Jan. 27 the rebels in Nicaragua overran the main Salvadorean air base at Illopango and smashed five of its 14 helicopters, 5 fighter planes, and 5 C-47 transports.
On the next day, Jan. 28, President Reagan formally certified that the El Salvador government had made ''progress'' on human rights and proposed raising US military aid to $300 million for the 1983 fiscal year.
During the balance of 1982 the rebels continued to increase the range and success of their operations. In January of this year they had their best month yet, with a series of impressively large operations giving them control of substantial areas of the country. It had become a real civil war of mounting severity.
President Reagan decided to send his UN ambassador, Jeane J. Kirkpatrick, to El Salvador. She arrived on Feb. 9 for a three-day survey and came back favoring ever stronger US military support both for the regime in El Salvador and for counterrevolutionary insurgents now attacking Nicaragua from bases in Honduras.
But still the rebels keep on coming and Congress grows more uneasy and remembers Vietnam and wonders where all this will lead.
Last week it led to the dismissal of Thomas O. Enders as US assistant secretary of state for inter-American affairs, disclosure of White House intention to replace Deane R. Hinton as US ambassador to El Salvador, report of a step-up in the number of US military advisers based in Honduras, and the beginning of a training program for Salvadorean troops there.
Further increases in the amount of US military aid are expected.
Ambassadors Enders and Hinton are both experienced and widely respected career diplomats. Mr. Enders is to be replaced by Langhorne A. Motley, a former land developer, opponent of environmentalism, and Republican stalwart in Alaska.
Ambassador Hinton is reportedly to be replaced by Gerald E. Thomas, a retired US Navy admiral, a black, who is said to be a personal friend of William P. Clark, the President's principal adviser in foreign affairs.
In just a little over two years US aid to the embattled regime in El Salvador has mounted from a modest five US military advisers and a mere $5.5 million to something very much more substantial involving not only an attempt to bolster a failing right-wing regime in El Salvador. There is also assistance to right-wing regimes in Guatemala and Honduras and a growing effort to destabilize the left-wing regime in Nicaragua.
There is no end in sight yet.
As in Vietnam the steady increase in US military intervention seems to be paced by a steady and greater increase in rebel strength and success. Many observers of the El Salvador situation now take for granted an eventual rebel victory. Ambassadors Enders and Hinton are apparently being removed because they recognized the possibility of military failure and recommended considering a return to diplomacy in search for a compromise political solution.
As Mr. Reagan plunges deeper into Central America, he resembles a captain who has sacked his experienced mates and replaced them with men who may be excellent in other fields but have no training in steering the ship through the swells ahead.