When Philippine security men arrested leftist union leader Felixberto Olalia on presidential orders at his home last month for an alleged plot against the government, they stormed through the house and carted away a truckload of books, papers and other belongings.

But what most upset the 79-year-old union leader and longtime communist, according to one of his lawyers, was the seizure of his prized collection of Playboy and Penthouse magazines.

"They were hardly an incitement to rebellion, but they may have been an incitement to something else," said the lawyer, Rene Saguisag.

He uses the anecdote to argue that even though the authorities' have broad powers of search and seizure, they have failed to turn up the evidence to prove their assertion that Olalia and 67 others were involved in plotting a wave of strikes, assassinations and bombings that allegedly were to culminate in the overthrow of President Ferdinand Marcos' administration next year.

Whatever the truth, it is clear that the crackdown on the dissident labor movement has reined in, at least for the time being, an increasingly troublesome sector of society over which the government long has felt it lacks adequate control.

The crackdown also smothered the threat of embarrassing nationwide strikes planned for this month during Marcos' important state visit to the United States.

According to Western diplomats and Philippine observers, the showdown had been brewing several months before Olalia's arrest Aug. 13. Authorities were annoyed by persistent labor unrest since martial law was lifted in January 1981 and blamed leftist union organizers for fomenting strikes.

Although fewer strikes have been staged this year than last, they generally have lasted longer and have cost nearly twice as many man-hours, according to government statistics.

The first warning shots against the unions were fired this spring when government-oriented newspapers splashed their front pages with stories of links between some Philippine labor leaders and foreign backers. The campaign abated after a few days.

Then in a May Day speech, Marcos blasted "elements in the labor movement who advocate the use of violence and defiance of law, who seek to turn collective bargaining into a bloody civil war."

The next month, the government was alarmed when 9,000 workers allied to Olalia's May 1 Movement labor confederation staged a sympathy strike in the vital Bataan export-processing zone for 54 workers who had been jailed for illegal picketing.

Although the strike lasted only three days, it caused great concern because it closed 18 of 55 factories in the zone, an export-oriented manufacturing area where the government is trying to attract foreign investment. In the view of government officials, the strike thus showed a potential for serious labor troubles stemming from minor incidents.

The final straw evidently came in July when Olalia and other labor leaders agreed to call a one-hour general strike in September to protest price increases, alleged police brutality and a new law that tends to limit workers' right to strike. Observers believe it was the prospect of strikes for purely political motives that provoked Marcos to crack down.

The charges that the labor leaders planned a subversive terrorist campaign have been greeted with some skepticism here, especially since authorities have not made public the evidence they say they have, according to Western diplomats. Instead, government accusers have cited Olalia's radical public speeches going back to last year, prompting some critics to question why he was not arrested earlier.

"It seems questionable that anything unusual was taking place," said one Western diplomat. In any case Olalia's group, which claims 1 million members but probably has no more than 200,000 dues-paying adherents under collective bargaining agreements, was "unlikely to be able to carry off any large-scale strike," the diplomat added.

Marcos' opponents and supporters alike generally agree that the timing of the crackdown has served to remind Filipinos that the 65-year-old president is still very much in charge and can still act decisively against any perceived threat. Beyond that, however, other suggested motives vary.

"Our reading is that this is an effort by Marcos to assure foreign investors they can count on him to provide cheap, controllable labor in this part of the world," Saguisag said.

Another supporter of Olalia, former senator Lorenzo Tanada, has called the case "basically nothing more than classic union-busting" with a "veneer of subversion" over it to gain support for the government's actions from conservative Filipinos.

For their part, government spokesmen insist that the crackdown is not meant to discourage legitimate union activity. A union whose leadership generally supports the government, the Trades Union Congress of the Philippines, has not been affected by the crackdown. Out of a total labor force of 18 million, it claims the adherence of more than half the Philippines' 2 million organized workers.

Olalia and his associates "were not arrested because they're labor leaders but because they're suspected accomplices or masterminds in a plot to overthrow the government by force," said Information Minister Gregorio Cendana. He added that "the government has an obligation to preserve itself."

Although Olalia was arrested under a presidential order that allows for indefinite detention without bail, there are signs that military authorities may be willing to release him for health reasons until his trial. According to his lawyers, the aged union leader became ill in detention and had to be moved to a military hospital here for a while.