As the dust settles on Spain's failed military coup, it is clear that the threat of dictatorship remains a factor in Spanish politics and that democracy here has not yet won an irreversible victory.

Many Spaniards believe last week's events were just a trial run. Consequently, senior politicians of all parties are saying that to avert a military takeover, the pace of change in Spain's fledgling democratic system must slow down.

Mass nationwide demonstrations were held Friday in favor of democracy and the constitution. The turnout was particularly high in Madrid and Valencia, where the military presence was most directly felt. But the plotters involved in the attempted takeover are not without their friends. Graffti on buildings here and elsewhere in Spain say of the mustachioed Civil Guard lieutenant colonel who led the assult on parialment: "Long live Tejero."

Admiration for the machismo of Lt. Col. Antonio Tejero and others is widespread among the extreme right. Secret collections for needy relatives of arrrested plotters are reliably report to be under way among some Army units.

The Madrid press reported that detained participants are being treated with deference in military garrisons holding them and are allowed visitors and telephones. The extreme rightist political leader Blas Pinar told an enthusiastic 3,000-strongly rally in the southern town of Murica at the weekend that such military prisons are "temples of honor."

The failed coup conceivably could have humiliated the military and its fantasies for power. In fact, the opposite is nearer the truth. A cowed political class is heeding King Juan Carlos' advice not to probe to deeply into the ramifications of the attempted takeover despite increasing evidence that prior knowledge if it was extensive. The failed coup was in any case not bungled. It failed because Juan Carlos refused to go along with it and in so doing threw the insurgents into confusion.

A socialist member of parliament graphically described the present limbo of Spanish politics as "democracy in chains." He explained that the Socialists, who form the main opposition party, can no longer act as a coherent parliamentary opponent of the ruling centrists.

The parliamentary left is all too aware that it cannot push for speedy resolution of complex constitutional issues such as consolidation of regional automomous governments. Nor can it tackle controversial social problems such as a divorce law or increased state education in place of church schooling without standing accused of antagonizing the military.

This reasoning was expounded at a closed-door meeting of the Socialist Party executive and led to a proposal by party leader Felipe Gonzalez that the Socialist join forces with the centrists to form a national coalition government -- a call rejected by Premier Leopoldo Calvo-Sotelo.

For the Socialist themselves, the proposal to enter the govrernment ran counter to their strategy throughout the last four years. They had hitherto said they preferred to be a constructive opposition and await their turn. But as Gonzalez told a press conference: "The red lights have now been switched on."

The coalition government idea was echoed at a lunch for journalists given by the conservative politician Manual Fraga Iribarne, who heads a minority right-wing party. Fraga bitterly attacked the premier's pretension to govern alone and said that unless there is a profound restructing through a coalition including his own party, the danger of a renewed coup attempt will continue.

"The reasons behind the coup remain: terrorism and the absence of valid spokesman between the military and parliament and between the military and the king," he said.

At the center of "second-coup-around-the-corner" fears is general agreement that the Feb. 23 drama involved more than just a crackpot coloned and a hotheaded general. Although there is almost certainly going to be no deep investigation of the tacit support the coup plotters received, it is unquestioned by the public that virtually the entire armed services at significant command level wavered between the insurgents and the constitution until it became clear that Juan Carlos was not behind the takeover.

Reliable sources close to the Army say that the majority feeling in the services is against exemplary court-martial sentences for the four generals and about 20 officers under detention.

Crucial to rebuilding trust is that there should be no civilian witch hunt among the armed forces. That was the initial message that Juan Carlos gave the politicians the day after the coup, and he repeated it again at the weekend in a key public speed before assembled officers at the Zaragoza Military Academy.

For the politicians the main task ahead is, as a centrist member of parliament privately admitted. to restore the credibility of representative government. The source than explained that this was a "Catch 22" situation since the only way of properly regaining respectability by carrying out a through investigation that would root out nondemocrats in the Army.