War and Remembrance makes formidable demands of viewers, and not just in terms of time. The concluding five chapters of Herman Wouk's harrowing epic will be shown on ABC (Ch. 4) starting Sunday night at 7 p.m. The total air time is 11 1-2 hours, added to the 18 hours that aired in November.

In addition, this fictionalized account of the last two years of World War II (from November, 1943, through August, 1945) includes lengthy and unflinching sequences set in Nazi concentration camps at Theresienstadt in Czechoslovakia and Auschwitz in Poland. The Auschwitz sequences, in parts XI and XII (Wednesday, May 10 and Sunday, May 14) were actually filmed at the camp, which now stands as a memorial to those who died in the Holocaust.Yes, the demands are great. But so are the emotional rewards. "War and Remembrance" ranks as a landmark achievement in the modern history of television.

ABC will precede Sunday night's opening installment, and the Wednesday episode, with advisories warning of graphic footage. Part IX, on Monday night, ends with an especially nightmarish sequence in which Nazi SS men threaten to murder a child in front of its weeping mother.

The story of that mother and child is the thread that holds "War and Remembrance" together. Jane Seymour, in the performance of her life, plays Natalie Jastrow, an American Jewess trapped in Europe during the first seven chapters and now fighting for the survival of herself and her son, Louis. She continues to grasp at hope in the face of unspeakable horror.

Imprisoned with her is her uncle Aaron, a once-patrician Jewish scholar played unforgettably by John Gielgud. As their situation grows more bleak, their fortitude increases and Aaron rediscovers the religious faith he had all but abandoned. The haunted face of Seymour - peering through barbed wire in a railroad boxcar, singing her little boy a Jewish lullabye - serves as a symbol of all those who suffered and millions who died.

What keeps one watching is concern for the fates of Natalie, Louis and Aaron. Indeed, the other stories being told sometimes seem ludicrously trivial by comparison. Among these is the marital ordeal of Adm. Victor "Pug" Henry (Robert Mitchum) and his flibbertygibbet wife Rhoda (Polly Bergen), complicated by Pug's affair with the beautiful Brit Pamela Tudsbury (Victoria Tennant).

Mitchum stalks the film emotionless and stoic, but this is supposed to be part of Pug's character. "Well, say something, Pug," his wife implores. "Don't just sit there like a sphinx!" Bergen's performance has an affecting nervous pathos, right to the bitter end. And in the role of Pug's son Byron - Natalie's distraught husband and a submarine commander in the Pacific - Hart Bochner again proves himself a solid leading man.

There are so many other notable performances it would take a telephone book to list them. Adolph Hitler is not an easy role to play, to put it mildly; Steven Berkoff does a chillingly original job of it. Milton Johns as Adolph Eichmann is similarly unnerving. Some will say the Nazis are played too broadly, as caricatures of evil. But caricatures of evil is what they were.

The press made a big deal out of the fact that "War and Remembrance" earned smaller ratings than expected when the first 18 hours were shown in November. However, it averaged an 18.6 Nielsen and a 29 percent share of the viewing audience - numbers that are not small. ABC estimates that more than 75 million people saw all or part of it. By contrast, 140 million are estimated to have watched its predecessor, "The Winds of War," in 1983.

In fact, "War and Remembrance" is much tougher to watch. Dan Curtis, the executive producer and director, and Wouk, who also worked on the script, could have made the miniseries much more accessible (and, arguably, more popular) by downplaying the concentration-camp scenes and playing up battles and romances. But they didn't. They knew that the story of the Holocaust was the most important story to tell, and they have dared to tell it in devastating detail.

Whether or not the miniseries proves to be a ratings blockbuster is utterly insignificant compared to the tremendous effort it represents and the uncompromising way in which it has been filmed. "War and Remembrance" is television of power, passion and courage.

What Wouk and Curtis want us to realize is that these scenes of life and death from decades ago also happened mere moments ago, that the dark forces unleashed by Hitler and the Nazis still exist in the world.