SOME OF the nation's young who came to Washington back in the '60s and early '70s to march and lie down in its streets in protest against the war in Vietnam sometimes stayed on into their thirties and became reporters and senate aides and bureaucrats and political gadflies. The Stockman generation, they might be called.

And some of the Cubans who managed to survive both the Bay of Pigs, and the CIA, later settled in Miami and turned to other pursuits, sometimes mundane, sometimes not. Those who spurned the quiet like occasionally went in for dope smuggling, espionage, informing and assassination.

They are two worlds of endless political intrigue and Taylor Branch jells them nicely in this rather long, but deftly written novel about a rich assortment of characters who range from an FBI agent's 90-year-old aunt to a half-Cuban, half-American veteran of the Bay of Pigs.

But the novel is mostly about a clutch of thirtyish male and female Washingtonians who move in and out of each other's lives and beds, talking endlessly to each other about their failed hopes, failed loves, and their growing disenchantment. The Cubans talk a lot too, mostly about themselves, but also about the CIA and the FBI and the DEA, which they despise almost as much as they do Fidel Castro.

Author Branch has crafted a plot of sorts, but his subplots, asides, incidents and set pieces often get in its way. Yet the resulting pastiche can nevertheless be enjoyed because Branch has an excellent ear for dialogue and an almost unerring gift for satire. Anyone who can label World War II as the war that was on the radio has as assured future.

The plot has to do with David Howell, a writer who works for a magazine that sounds suspiciously like The Washington Monthly. Howell, more or less on assignment, drifts down to Miami and into a weird dope dealer's elaborate establishment. Later, he encounters the notorious Cuban, Carlos Marana, who reeks of intrigue and espionage and death. Acting on a tip from Marana, Howell almost witnesses an assassination of another Cuban in Miami. He flees Miami and returns to Washington only to be drawn more deeply into the web of double-dealing when Marana tips him off about a purported plot to assassinate the U.S. secretary of state in Venezuela.

Howell, with a friend, goes to the State Department where he spins out his fanciful tale. Precautions are taken, the secretary is unharmed, Marana is more or less exonerated o past misdeeds and retires into respectable cocaine smuggling. But there is yet one more violent, senseless death to come, and it is this death that drives Howell and his wife-to-be out of Washington and into the relative seclusion of Harpers Ferry.

The principal trouble with The Empire Blues is its characters' almost continuous self-examination. Although it is often both sprightly and amusing, too much soon becomes wearisome -- like eavesdropping on a four-hour group therapy session where the problems don't seem all the grave or insoluble. After a while, impatience replaces sympathy -- and interest.

But when things begin to get too soggy, Branch's humor almost invariably comes to the rescue. He is at his best when describing the major and minor foibles of Washington's public and private bureaucracies. There is the sobersided reporter, for example, who fears for his career because his swearing isn't quite obscene or heartfelt enough. There is the FBI agent who, despite his narow feet, has always worn overly wide shoes because the Bureau feels that slim narrow feet denote effeminacy -- or worse.

And finally there is Branch's understanding of and obvious sympathy for the young who came to Washington to protest a war and stayed on to become, in a few instances, the very people they demonstrated against.

It's a novel about the price that is paid for growing up in a highly charged political atmosphere. If the price is often disillusionment and disenchantment, Branch seems to feel that it was all somehow worthwhile.

Two of his attractive characters finally trade in what little ambition they have left for a quiet, almost reflective maturity. Branch certainly makes it sound like no bad deal.