Rock-solid as drama, rickety as history, and crudely fascinating as speculative fiction, "Blood Feud," a four-hour, two-part movie about the power struggle between Robert F. Kennedy and former Teamsters boss James R. Hoffa, leaves one feeling shaken, suspicious--and depressed. The movie could prove to be the catalyst for a wide-scale paranoia revival, because it ascribes to organized crime virtually unchallengeable power and control over American life.

As programming, the film, at 8 tonight and tomorrow night on Channel 20, blasts everything on competing channels right out of the water, mainly by dealing with subject matter that is not only still extremely volatile but also, surely, of more than passing interest in Washington. Channel 20 could have shown the film as early as April 23, but saved it for the May ratings "sweeps."

"Blood Feud" prowls the back alleys of Camelot, dramatizing the thesis, outrageous or not, that President John F. Kennedy was assassinated by the Mob because his brother Bobby leaned too hard on Hoffa, whose ties with the Mob were intimate--ties that eventually, according to this film, strangled even Hoffa. Near the end of the picture, a Hoffa desperate to stay out of jail and fearful of the Mob's omnipotence moans, "I can't get out, even if I wanted to," and tells then-Sen. Kennedy by telephone, "We both made a lot of big enemies, Bobby."

The screenplay, by Robert Boris, states that Hoffa had a highly placed informant within the FBI, that J. Edgar Hoover tricked then-Attorney General Kennedy into authorizing wiretaps far more extensive than Kennedy thought he was approving, and that the CIA worked "hand in hand" with the mob on a plan to assassinate Fidel Castro. Robert Kennedy is alleged to have said, "Sooner or later, everyone does business with everyone."

Earlier, after Mob leaders determine that President Kennedy looks certain to be elected to a second term, in a major confab at a fancy restaurant, one of them says, "So, we must deal with the problem directly," and another says, "That's right--anything can be done, no?" He is echoing a speech from "The Godfather" in which Michael Corleone declares, "If history has taught us anything, it is that anyone, anyone, can be killed."

"Blood Feud's" brand of political paranoia has not been in vogue for years, except, of course, with the conspiracy subculture that continues to ask largely unanswered questions about the Kennedy assassinations. It certainly doesn't pass the test for cool in the '80s. If something can be refreshing in a sordid way, "Blood Feud" is. It isn't a ride with Mr. Toad through Cloud Cuckoo Land like "Executive Action" was a few years ago, nor does it come across as a quack's tract, because Boris is also telling a story about a specific personal conflict, that between Hoffa and his nemesis Kennedy.

In terms of historical accuracy, that conflict is surely inflated wildly out of proportion--"Blood Feud" indeed! Boris never even makes the alleged origins of the "feud" particularly clear, except that Hoffa is forever impugning Kennedy for his wealth and privilege. He refers to him during the film as "a damn bootlegger's son," a "rich punk" and "Little Lord Fauntleroy" in addition to more generic epithets like "slimy little runt," "that little worm," "that arrogant runt" and "that little rat."

But the crucial thing about "Blood Feud" is that one may dismiss its interpretation of history as Hollywood hooey (not that the theories about Mob complicity and Mob-CIA ties are undocumented elsewhere) and still find all four hours gripping, electric and on some useful level disturbing, in part because writer Boris and director Michael Newell keep a taut, taut ship and largely because, as Kennedy and Hoffa, actors Cotter Smith and Robert Blake are sensationally strong and consistent.

They are required to storm through confrontation after confrontation (this is not "talking head" television so much as shouting head television) including some that probably never occurred, and yet their portrayals have, beneath the bravado, palpable subtleties and a basic shrewdness that keep one riveted even though Hoffa's rantings and ravings eventually become almost comical. Boris has the two men going mano a mano, face to face, no fewer than six times, including alleged encounters at which no one else was present.

Handcuffed at last, though on a charge he would later beat, Blake's Hoffa snarls up at Smith's Kennedy in part one and says, "Don't break out the champagne yet, kid. We got a few rounds to go. See, this is for the heavyweight championship of the world now." Later, after riding alone on an elevator with Kennedy (and insisting that the two men show each other the family photos in their wallets) Hoffa screams more macho taunts as Kennedy walks down a hallway: "This is not touch football at Hickory Hill!" And, "Hey, Bobby! Hey, Bobby! Get ready for the next round, kid!"

If it sounds laughably unlikely, the eternally pugnacious Blake and the scrupulously sensitive Smith (in his first major role) make it play quite convincingly. And while Hoffa is indeed depicted as a "thug," as his son has charged--even refusing to lower the flag in front of the Teamster building to half-mast in memory of President Kennedy--he also becomes, in the final two hours, a poignantly trapped, doomed, hopelessly corrupted warrior. He demolishes his own office looking for the planted listening device he can never find, even as a jury is indicting him on five counts of jury tampering, and when he finally is led into a jail cell in 1968, after years of appeals and delay, Blake looks so crushed and terrified that it is painful to watch.

The film covers 11 years in the lives of these combatants, in scenes that alternate between them. At first, things do not look encouraging for the film. On a sailboat supposedly floating around Hyannisport, Joseph Kennedy, John and Robert are seen casually planning the future and even kicking around the subject of Mob ties to organized labor--the kind of conversation one doubts ever got conversed. Credibility is repeatedly ravaged by the presence of non-actor Sam Groom as John Kennedy; his flabby, lazy portrayal isn't even good enough to pass for a bad nightclub impression. Groom ruins every scene in which he appears.

Fellowship between the Kennedy brothers is depicted so falsely, and Groom is so maddeningly uninvolved in his role, that for a while the picture plays like "The Hardy Boys Meet Hitler." But the relationships between Robert Kennedy and his staff, once he goes to Washington and starts working for the McClellan committee, are more believably drawn, and the image of these young, ambitious, shirt-sleeved scrappers plotting strategy in cluttered offices is an evocative one. Smith is bracing, alert and complex; his work is all performance, no impersonation.

Among the real figures portrayed in the film are Forrest Tucker as Lyndon B. Johnson (who refuses to shake Bobby's hand when they meet in the Oval Office), Ernest Borgnine in a gargoylish interpretation of J. Edgar Hoover (who explains that the FBI stays clear of the Mob because all who come in contact with it fall under the spell of its fortunes) and Jose Ferrer as lawyer Edward Bennett Williams (whose defense of Hoffa on a bribery charge includes a lacerating interrogation of Robert Kennedy on the witness stand).

The closing credits list McKee Anderson in the role of Ethel Kennedy, but she is nowhere to be seen. A spokesman for 20th Century-Fox Television said yesterday from Los Angeles that "Blood Feud" originally ran 5 1/2 hours, and that the scenes trimmed include all of those in which Anderson appeared. He denied the deletions had anything to do with objections to the film made by Ethel Kennedy in an April 12 letter to Al Masini, president of Operation Prime Time, syndicators of the program.

In her letter, Kennedy wrote that while she had not read the script, "I am familiar enough with the contents to know that it is unfair to Bobby" and characterized the film as one which "distorts history and is . . . lacking in integrity."

Of course, the film is a distortion, and it may be unfair not only to Robert Kennedy but to others depicted (some with changed names because they were not willing to be portrayed). And there is an aspect of grubbiness to the production; it isn't a gratifying experience, and watching it is a little like hearing salacious gossip--but gossip that is nonetheless irresistible.

If coproducers Daniel Selznick and Joel Glickman have logged any real achievement here, it is in producing a film that could conceivably jolt viewers into troubled new curiosity about how deeply organized crime has infected the American bloodstream. "The blood feud is over, but the war for power goes on," says the narrator at the conclusion. One of the hardest things to know in life is, how much paranoia is too much, and how much is just enough?