The crude reappearance yesterday of Katherine Boudin, the last well-known Weather Underground moll on the loose, broke the reassuring pattern established in recent years by other aging militants.

Mark Rudd, Bernardine Dohrn and Cathlyn Platt Wilkerson have crept rather tamely out of hiding one by one, their menace seeming to shrivel and fade in the light.

Targeted by J. Edgar Hoover's FBI a decade ago as members of a New Left guerrilla youth movement that threatened national security by fomenting violence and terrorist attacks on government institutions, they later emerged in an altered climate, accepted light or suspended sentences and blended back into the society they had condemned.

Only one--Wilkerson--is in prison today.

Meanwhile, in another slow dying echo of the period, top FBI officals were convicted of breaking the law in order to pursue them and, last April, pardoned by President Reagan.

Silas (Trim) Bissell is the only Underground fugitive still fleeing a federal charge, FBI officials said yesterday. He is accused of bombing an ROTC building at the University of Washington in 1969. Another, Jeff Jones, is sought on a state charge for a "bomb factory" incident in Hoboken, N.J., in 1979.

Boudin and Wilkerson had exploded into the national consciousness in early 1970 when a bomb went off and leveled a fashionable Greenwich Village townhouse owned by Wilkerson's advertising executive father, killing three people. The lingering public vision of the two young women was as witnesses last saw them--scrambling out of the falling debris in the red afterglow, one completely naked, one wearing only a pair of blue jeans. Then they disappeared for a decade.

The townhouse, officials said, had been an Underground bomb factory. The rubble yielded 60 unexploded sticks of dynamite and 100 blasting caps, along with the three corpses.

Boudin's arrest yesterday, this time as she fled a sensational armored car robbery and triple murder near Nyack, N.Y., evoked some of the old fear and loathing at the same time that it answered a question not even asked much anymore: whatever happened to Kathy Boudin?

In July, 1980, Wilkerson surrendered in Manhattan to face felony charges stemming from the explosion and is currently serving a three-year sentence. Her incarceration was delayed so that the 35-year-old mother could find someone to take care of her 3-year-old.

Then last December in Chicago, Bernardine Dohrn, a University of Chicago graduate who had once topped the FBI's "most wanted" list, held a news conference to talk once more of "unspeakable crimes" by the U.S. government, and surrendered.

She pleaded innocent to charges growing out of the 1969 anti-war demonstrations in that city known as the "Days of Rage," in which stick-wielding radicals smashed windows and dented cars as they eluded police.

She and another Underground leader, William Ayers, son of a former president of Chicago's Commonwealth Edison Co., were given suspended sentences. The New York Times reported at the time that the pair had been living on Manhattan's West Side for two years and that Dohrn had been working as a waitress.

When Underground leader Mark Rudd performed his own Rip Van Winkle act in 1977, surrendering in Manhattan, he had just turned 30 and was keeping his political views to himself.

Instrumental in shutting down Columbia University in 1968, Rudd had become the basis for a Doonesbury character named "Megaphone Mark." He was fined $2,000 and placed on two years' probation for his role in the 1969 "Days of Rage" in Chicago. He was last reported working and going to school in the Southwest.

Also captured yesterday was Judith Clark, another Underground figure, who had been caught before in Chicago and released, officials said.

The Weather Underground began as the Weatherman, a title taken from the Bob Dylan song lyric--"You don't need a weatherman to know which way the wind blows." The name reportedly was changed to satisfy female members. The group was an offshoot of the Students for a Democratic Society, founded in 1962.

Members are said to have maintained contact with each other, aided by a support system of allies. But surfacing members have consistently refused to reveal details of life underground.

Said Wilkerson after her sentencing, "Given the choice of prison or cooperation with the perpetrators of global violence, I chose to join the folks inside, for they are my people."