Something seems to happen when April and spring finally arrive in Washington, and so it has again.

In years past, this loveliest of seasons saw the capital grappling with the sudden shocks of the deaths of Lincoln and Franklin D. Roosevelt, total defeat at the Bay of Pigs, final agonies of the fall of Saigon that ended the embittering Vietnam experience. Now the events of this April vividly call to mind another difficult period just 20 years ago.

That's when Lyndon B. Johnson, at the peak of his popularity, after winning the greatest landslide since FDR's in 1936 and displaying a mastery over the Congress as had few presidents, was wrestling with the decisions that led to the greater commitment of American military power around the world.

First came the dispatch of Marines and soldiers into Santo Domingo in the Dominican Republic at the end of April, an intervention that shocked many of his supporters and prompted the first searching congressional examination of his foreign policies by J. William Fulbright (D-Ark.), who was chairman of the Senate Foreign Relations Committee. Then came the steady escalation of the war in Vietnam (the U.S. bombing of North Vietnam had begun two months earlier) as more and more troops were sent to fight there. Suddenly, that trickle of a military commitment became a flood that eventually engulfed and destroyed Johnson's presidency.

Now the Reagan administration, flush from its great political victory of November and emboldened by continuing dominance over Congress, has embarked on a course that eerily evokes memories of that earlier, troubled spring. The president sounds as if he's on a holy crusade. His aides speak darkly of calamities that will occur if we don't support the "contras" in Nicaragua. From them, and Reagan, a new version of the domino theory emerges: Unless we stop them there, and now, the borders of Central America will overflow, the communist tide will move inexorably north and sweep into the United States, the Soviets will stand astride the Panama Canal and they'll establish a nuclear submarine base at Cancun, Mexico, to hold sway over the Caribbean.

The administration seems trapped -- or perhaps intoxicated -- by its rhetoric. It's letting ideology triumph over good sense. In so doing, it's picking needless fights, angering friends as well as foes (the fiasco over Reagan's European trip stands as an almost unbelievable bungle by a group that prides itself, rightly, on the proper application of PR) and drawing attention away from significant problem areas that require its most skillful handling and public support: the budget deficit, the trade deficit, the looming protection wars.

On top of this came an astonishing episode last week that reinforced the notion that the second Reagan term is letting its ideological impulses run amok.

This was the case of Eileen Marie Gardner, named by Reagan's new secretary of education, William J. Bennett, to head a newly created Office of Educational Practice and Philosophy. Gardner immediately attracted headlines and critical editorials after her extraordinary views on whether the public has an obligation to aid the handicapped -- she's against it because, among other reasons, the handicapped "falsely assume that the lottery of life has penalized them at random" -- were aired in a Senate hearing chaired by Lowell P. Weicker Jr. (R-Conn.).

Gardner didn't last long. After testimony of an even more controversial nature, the appointment was quickly dropped. But this kind of appointment reveals a cast of mind that seems pervasive at the top levels of the administration: that of true believers determined to impose their rigidly held views of God and society on the rest of public life.

For example, here's what Gardner wrote in a background paper for the Heritage Foundation, a conservative research center influential in Reagan administration circles, about "The Federal Role in Education":

"The educational debacle which confronts this nation is directly attributable to its guiding philosophy of the last 25 years -- a philosophy . . . which rests upon false assumptions about the basic nature of man and the purpose of man's existence . . . . Too many of those who have formed and/or continue to support present education policies and programs do so, either consciously or unconsciously, from the false assumptions that man's purpose and end are defined by man and that consensus determines what is right and good. If man determines his own end, then equality of result should be attainable by man's manipulation of man. Thus, we have experienced an explosion of social legislation and court decisions to attain that end . . . . "

She went to say:

"All men are equal insofar as all men are emendations from God. However, not all men have yet attained the same manifest level of development. Every man is evolving along his own path, from his own efforts, hopefully upwards to goodness through truth; not all men are at the same level of development, awareness, or ability -- nor are they meant to be."

Out of all this woolgathering, this intellectual zealotry, this rejection of the ideals of public service, this would-be public servant picked for a public role in the Department of Education concluded: "The proper role of the federal government in education is no role . . . . "

If that's the kind of thinking that gets rewarded with high administration posts this spring, then we're witnessing nothing less than an attempt to return to the concepts of "Social Darwinism" and laissez faire in public life.

"Social Darwinism" is the discredited cast of mind that permitted the robber barons to celebrate their crushing of the little people by claiming it was all the workings of God's immutable laws. In that reasoning, you measure success by the survival of the fittest. What counts is strength and power. Sink or swim. If you fail, it's your fault. Government and society have no obligation to help those in need or those who are weaker.

Of course, that kind of political thinking went the way of the dinosaurs, but its reemergence fits in with the cross-currents of this loveliest and cruelest month in Washington. For the Reagan administration, the events of this month ought to draw another lesson. This is the month, also, where, in years past, presidents came a cropper by overreaching themselves in asserting their powers and in misreading their popularity.