Two years ago, ABC News, and to some extent news departments at other networks, were humiliated when an ABC entertainment program, "The Day After," the famous grim fantasy about nuclear Armageddon, provoked more thought and generated greater hubbub about an urgent national topic than did any news broadcast that year.

Indeed, during the same week that "Day After" aired, ABC News devoted the full hour of its "20/20" news magazine to a reverential consideration of pop star Barbra Streisand. The contrast was embarrassing.

Perhaps at that moment the wheels were set in motion for the dauntingly ambitious, exhaustingly exhaustive three-hour ABC News "Closeup" that airs tonight, "The Fire Unleashed," a study of the nuclear age and all its intimidating possibilities, at 8 on Channel 7. A wealth of information arranged with illuminating coherence, the program is nevertheless not only oddly unmoving, but oddly unterrifying as well, even though the specter of annihilation, among other specters, is invoked at fairly regular intervals.

Unquestionably a logistical achievement, and a commendably herculean effort, the program suffers most from miscalculations of style. The level of portentousness is kept so high that what should be startling or engrossing becomes finally rather numbing. Simply showing so many nuclear explosions and missile launchings diminishes the power of these images. In addition, nearly everything in the program is not just underscored but hyperscored with a musical soundtrack that ranges from "Inner Sanctum" spookiness to spaghetti Western pop-lyricism. There was probably a more sparing use of dramatic music in the dramatic production "The Day After" than on this news show.

In addition, the script, much of it read by reporter and writer Marshall Frady, seems overblown from the word boom. Near the top of the program, Frady intones, "Out of the vast energies of the universe, from the great engines of creation, our planet was formed, a small bright globe, isolated in the measureless void of space." Near the end, he is still intoning: "Over the great reaches of cosmic time, we have existed here for only a moment, creating against the void around us an urgent and tumultuous pageant . . . "

Someone forgot that television is not a word medium but a picture medium. The single most eloquently communicative instant within the entire three hours occurs in the third, when the uncertainties of the arms race are likened to a tightwire act. Prokofiev is on the soundtrack, and the camera shows acts from a Russian circus intercut with shots of explosive weaponry. The wordless simplicity is piquant. Then Frady returns to make the metaphor literal and prosaic. For a few seconds there, they had something going.

ABC News, perhaps unjustifiably at this point, is generally considered the glitziest of the three network news operations. No one could call tonight's documentary "The Glitz Unleashed." This is not the usual glittery kind of glitz. Instead, the program may qualify as documentary television's first example of Glitz Gothic.

The report is divided into four sections. "Nearing Armageddon," the first, details alarming increases in global nuclear proliferation. "A Power to Light the World" chronicles the sorry history of the nuclear power industry. "The Quiet and Lethal Legacy," Part 3, is about the nuclear waste that will outlive us all.

"The Apocalypse Game," the concluding segment, is the most compelling and immediate, since it deals with the U.S.-Soviet arms race. There is little fruity prose here, and the restive musical cues relax a little as Frady and such authorities as former defense secretaries James Schlesinger and Robert McNamara talk about how the superpowers plot strategy also to plot destruction. This final sequence will likely be the most controversial of the four, because Frady takes what clearly seems a hostile approach to the Reagan Administration's so-called Star Wars plan for outer space defensive weaponry.

Frady gives the impression that Star Wars is a scheme sold quietly to President Reagan in the dead of night by nuclear physicist Edward Teller. "In March of 1983," Frady says, "without consulting the broad scientific or defense community, Ronald Reagan launched Star Wars." The "most ambitious weapons system in human history" is based upon "a long-discounted strategy," Frady says.

The program seems to give greater weight to Star Wars critics than to Star Wars defenders like Secretary of Defense Caspar Weinberger. It is this fourth segment that provoked the conservative weekly Human Events to dismiss all of "Fire Unleashed" as "more anti-nuclear propaganda" from ABC. Yet it is precisely because of the strong viewpoint that the last quarter of the program works so well. Fairness does not mean sterile objectivity; the broadcast is fair, but not objective. Time for additional discussion will be provided by "Nightline" at 11:30 p.m.

After a weightily ominous prologue that brings to mind the "Rite of Spring" sequence from "Fantasia," the proliferation segment, most hard-newsy of the four, documents the spread of nuclear weapons to countries that either have them now or will have them in a deadly twinkling. Former president Jimmy Carter is among those testifying to the escalating dangers. A segment on India and Pakistan is particularly timely in light of Indian Prime Minister Rajiv Gandhi's charge, reported yesterday, that the United States is taking a "soft line" toward Pakistan's efforts to arm itself and his warning that India will develop its own bomb if necessary.

Frady says that the bomb is now considered a status symbol representing "instant arrival as an important power" to countries that acquire it. The chilliest comment is from Syrian Defense Minister Mustafa Tlas: "The nuclear weapon is to a state that seeks to defend its independence like a gun is to a cowboy."

The segment on nuclear power begins, not very subtly, with lightning bolts and cracks of thunder. Cameras visit the site of the Three Mile Island disaster of 1979. Humans and animals have both felt the lingering effects of that near-meltdown; there is a disheartening shot of a kitten staggering drunkenly toward its dish of milk. Construction of nuclear power plants in this country is a continuing scandal marked, Frady says, by "stupendous cost overruns," "careless construction practices," "inexperienced management" and "the worst human safety record in the Western world."

There are no glad tidings, either, in the segment on nuclear waste. It did take guts for ABC to cram this much bad news into a single night of TV.

ABC expects a certain amount of praise merely for undertaking a project as mammoth as this. So be it.

For the record, NBC News invented the three-hour documentary and NBC was the first network to devote its entire prime-time schedule to a single subject: "The American Revolution of 1963," on the civil rights struggle, which aired Sept. 2, 1963. The ABC broadcast tonight is still not as substantial a production as "The Defense of the United States," a five-hour, five-night documentary aired by CBS in 1981. And no one in TV news, producers of "Fire Unleashed" included, has yet come up with a more graphic, memorable way to impart the devastating effects of a nuclear attack than did NBC News for a 1979 special on the Salt II talks in which John Chancellor simply roamed around Kansas pointing out to viewers which places and things would be obliterated and which incinerated.

Various producers contributed to "The Fire Unleashed"; Pamela Hill is in charge of the "Closeup" unit and Richard Richter is senior producer. Frady is spelled at a few points in the program by Peter Jennings, who provides introductions to the introductions to each segment.

While "Fire Unleashed" is a broadcast in which the network can take pride, one can't help imagining how much greater its effect would be if the resources of television had been more gainfully and less theatrically employed. Still, between those "vast energies of the universe" and those "great reaches of cosmic time," there is much here to engage the mind -- and trouble the soul.