'Last Days of Pompeii' is overblown; 'Final Battle' is not the end

The choice on TV this Sunday will be the 28th century AD or the 1st century AD. Insidious aliens from another planet stealing Earth's water and kidnapping earthmen for their own planet's food supply - or dissipated Romans turning thumbs down on slave gladiators in the arena and engaging in Bacchanalian orgies in the baths.

Yes, the first week of May ushers in another ''Sweeps'' month, when advertising rates are set for the next three-month period based upon local ratings as measured by Nielsen. So, as usual, the networks have saved some of their biggest guns for this period: ABC is offering The Last Days of Pompeii (Sunday, May 6, 8-11 p.m., Monday, May 7, 9-11 p.m, and Tuesday, May 8, 9-11 p.m.) and NBC is offering V: The Final Battle (Sunday, May 6, 7, and 8, 9-11 p.m.). CBS, with the self-assurance that comes from being No. 1 in the season race, is sticking with its regular programming for those days.

As usual, however, the shows have been scheduled with almost no regard for viewers who might want to see both, so you may have to tape one if you own a VCR , make a choice, or sample a bit of both. Or, perhaps, even decide to forgo both network choices and watch a fascinating dramatization of one of the most mysterious trials in recent history, the Alger Hiss perjury trials, which airs on PBS on May 7, 8, and 9 (9-11 p.m., see tomorrow's ''On TV'' column). ''The Last Days of Pompeii''

Seven hours of toga-etherness may be a bit much for most American TV-viewing families.

''The Last Days of Pompeii'' have a habit of recurring periodically on the screen, with productions appearing both in 1935 and 1959.

Now, this seven-hour version, produced by David Gerber Productions, is based loosely upon the original novel, with a screenplay by Carmen Culver. The miniseries, directed by Peter Hunt, and starring some fine actors like Franco Nero, Sir Laurence Olivier, Lesley-Anne Down, Linda Purl, and Anthony Quayle, depends on big-screen spectacle squeezed onto a small screen for its major effects. Pompeii is treated like a moral suburb of Sodom.

The show is a bit like a home-cooked Italian meal - be prepared for large portions of everything: violence in the form of gladiator battles, Christian-eating lions, complex love affairs, massacres of the Christian worshipers, etc. It's the old ''Golden Boy'' story with a poor Greek gladiator who wants to escape the arena, determined to fight his last fight and then rescue his father from slavery.

Ernest Borgnine plays the manager of the gladiator show like a Jewish mother running Rocky's training gym. Lesley-Anne Down, one of the most delicately lovely actresses on the screen, is once again miscast (in her last outing she was a gypsy and this time she plays a prostitute, determinedly but unbelievably).

There are innumerable subplots involving politics, religion, and economics as well as romance, all played before the supposed smoking backdrop of Vesuvius, which often looks suspiciously like a studio backdrop as the smoke from its crater remains stationary.

Viewers can learn much about day-to-day life in Pompeii, if one has the patience. But if you want to cheat a bit, wait until the final hour on Tuesday at 10 p.m. and you can see not only the eruption of Vesuvius and the mad dash to the sea to escape, but the tying together of the loose ends of just about all the many subplots. The last hour of ''The Last Days'' is quite enough. Figure you're not missing six hours, you're gaining them. ''V: The Final Battle''

When the original two-part ''V'' was aired last May, more than 65 million viewers saw all or part of the miniseries. Now, one year later, NBC is going back to the same aliens for more. ''V: The Final Battle'' is a six-hour continuation of that story about reptilian alien invaders from space who set about to conquer, dominate, and plunder Earth.

Only the first two hours was available at press time, but the hours I saw were promisingly intelligent - science fiction for a thinking generation. The show still makes valid social commentary on life on Earth, concentrating to a great extent in the first two hours on the easy manipulation of the news media by the alien powers.

Pinnacle Books is coordinating its release of ''V,'' a paperback novelized version of both shows by A. C. Crispin, and chances are it will be hitting the best-seller lists. I note that at the end of the novel readers are told to look forward to more in September: ''The alien forces hold all of Earth in an iron grip of repression and terror. But as long as one human soul struggles to resist , hope remains alive. The resistance grows as the saga continues. . . .''

So don't imagine that ''The Final Battle'' will actually prove to be the final episode of the ''V'' story. Remember ''Star Wars,'' Return of the Jedi,'' et al. The only thing that will kill it off will be bad ratings. And if you don't like the first episode next week, you can see to that.