THE CIVIL WAR, chief trauma of American history, seemed to settle the question that so preoccupied Lincoln: the continental republic would develop from coast to coast and no internal strain would be countenanced as the excuse for a collapse into a heap of duchies.

But nobody quite knew what the baby empire would grow into. The question is still before us, but the decades following the Civil War pointed to a strongly centralized superpower based on industrial strength, dependent on increasingly sophisticated communications and a concentration of money not known before.

Lenin was born in 1870, the year Lee died. Different countries, same planet.

General Grant, regarded by many as the military savior of the Republic, won reelevtion ot the presidency without grave trouble in 1872, and this suggested that brilliance is all very well, but hardly a requirement for high office. This suspicion was confirmed with the election of Hayes to succeed him.

For some time, it appeared, the nation was going to be more concerned with the West and with railroads, with pneumatic drills and telephones (both new) than with brilliance in the arts, including government.

The country began thinking grandly of itself and in common with much of the western world began to cover all surfaces with imperial crimson plush. (Victoria was proclaimed empress of India in 1877.)

Something of the new sense of power may be seen conveniently within one block on Pennsylvania Avenue.

The White House reflects in its architecture, no doubt, something of the clean style of the early Republic with its debt both to the eighteenth century and classical Rome as well.

Right down in the next block, however, sulks the Executive Office Building, a heroic monument to bombast and claptrap with columns stuck on like fleas and the general decor drawn from every human construction over 6000 years except the Indian wigwam. It is the result of wanting the best of everything. Without the foggies notion what that might be.

Labor began its rise to power, however feebly at first, in these decades following in the tide of industrial expansion and wealth. Railroads became a great force, and people nobody ever heard of began to be heard of. Colorado, of all places, was admitted to the Unionn in 1876 and bold spirits gingerly traveled to Denver in due time, taking grape jelly and tea in their suitcases on the theory that out there they probably ate raw buffaloes.

The presidential election of 1876 would have been a great scandal if the nation had been more sensitive to scandal. Tilden, the Democrat, won 184 electoral votes and Hayes, the Republican, won 165. But twenty additional votes were "in doubt," or up for grabs. At the time federal troops were in several southern states, presumably enforcing rights for blacks. Heyes assured the moderate South that troops would be withdrawn, and wound up with all the twenty hitherto disputed votes, to be proclaimed President three days before he took office.

This thwarting og the popular will (for Tilden won the most individual votes) again showed an ambiguity in the American way of electing presidents, and gave the new Washington Post, for example, a peculiarly sharp sense of outrage.

If anyone had viewed the nation from Mars, or other calm vantage point, he might have thought the nation was losing something of the vision of Jefferson.

Or, for that matter , Lincoln.

Yet ages further removed than our own may well look back to the decades following the war as a painful rite af passage (for charity appreciates along with increasing remoteness from the event) as painful and chancy as birth, when the nation moved from agriculture to industry, from cottage to factory, from mule to Metroliner. There are days, needless to say, when the course of progress seems less a swap than a swindle.

Despite what seems to us now tone, a slackening of principle, there were many indicators of the future:

Frozen meat was shipped from Argentina for the first time. The first elevated railway ran in New York. The first public phones were installed. (The first phone directory for Washington appeared in 1878, doubtless inspired by the establishment of The Post the year before and the consequent need to complain promptly.)

Great works by Wagner and Brahms appeared. Canned fruit - there is nothing like a canned peach when you're out in the woods - became available. Carnegie developed his first huge steel furnace. Chicago was burnt down - Mrs. O'Leary's cow, not a blast furnace, was blamed - but recovered to become hog butcher ot the world.

The United States surpassed France in population. Electric lights lit streets in New York. Johns Hopkins University was founded at Baltimore. The first American zoo opened in Philadelphia. The city of Memphis, plagued by yellow fever, shot off cannons to dispel effluvia from the swamps and scrubbed the sidewalks with acid. This is an example of vigorous local action to solve local problems, though unfortunately the plague was brought by mosquitoes, not noxious vapors, and the cannonballs hit few bugs.

Pasteur discovered a chicken cholera vaccine. Gilbert and Sullivan turned out Pinafore. Whistler the painter sued Ruskin the critic for a large sum and got nothing.

Pundits oftens say (quoting other pundits) that if we do not learn from history we are condemned to repeat it. Vaccine was learned, however, neither from the wisdom nor the ignorance of Aristotle, but by means of a new way of looking at disease. The past, after all, is full of conflicting adages but no sure guides for dealing with fossil fuels, say, or nuclear weapons, except suggesting that ruin is possible for good-hearted old empires.

If those decades following the war seem crowned with smugness and a certain coarseness of both architecture and soul, still nobody ever called them the heights of American dreaming. Or American style.