With the networks doing so few documentaries in recent years, and with the list of unexplored subjects virtually endless, how urgent is the topic of "Sex in the Soviet Union"? Urgent enough for there to be a one-hour edition of "The Koppel Report" undressing the issue, so to speak, at 10 tonight on Channel 7.

Koppel's specials, co-produced by his company and ABC News, haven't exactly been blockbusters in the ratings, and ratings are all networks -- even network news divisions -- care about anymore. So a report with the word "sex" in the title must have been seen as a go-get-'em proposition.

Whatever the motive behind it, "Sex" is not without value and certainly not without interest.

During a dizzy peep show montage that opens the program, Koppel endeavors to invest it with Higher Purpose. "The Soviet Union is spinning out of control" with its new glasnost-era freedoms, Koppel says, and the current blitz of sexual imagery bombarding Soviets is a reflection of "the far more profound changes that are convulsing that country."

So we'll be looking at political, economic and social problems "as seen through the prism of sex in the Soviet Union," saith Ted. Sex, a prism? Why not? TV journalists are very big on prisms of their own making.

Koppel spends most of his time in Leningrad, where he talks to: Soviet women who say they are too tired for sex after long days of standing in line for bread; wives who have had abortions, which are extremely common and used as a means of birth control ("I had eight or nine abortions and my mother had 19," one woman says); and a soft-spoken transvestite named Vladimir who was an outcast under communism but is something of a superstar now.

There's also a ragtag heavy metal rock group that features topless dancers onstage, and a longhaired young man who voices a common complaint about Soviet birth control devices -- "Using a Soviet condom is like smelling a rose with a gas mask on," he says.

While a law remains on the books prohibiting homosexuality, Koppel sees signs of liberalizing attitudes. He stops at a gay cruising spot in Leningrad and talks to some of the young men gathered there.

The least you can say for this hour is that Ted Koppel shows up in places where you would least expect to find Ted Koppel. A tie-less Teddy even interviews a Soviet madam, asking her matter-of-factly, "Can you explain to me how the business works?"

Dmitri Shalin, a very helpful sociologist, analyzes some of the changes taking place in the U.S.S.R., where the pendulum now swings wildly. Essentially what seems to be happening is that the Soviets are now going through The '60s! Heaven help them. They're going to need more than foodstuffs to survive that.

The funniest sound bites are from a hopelessly stereotypical bureaucrat, Deputy Interior Minister Stasys Lisauskas, whose every word and syllable comes directly from the Soviet past of double talk and statespeak.

Koppel seems a somewhat reluctant reporter on this assignment, and his narration has too many bossy viewer advisories ("Brace yourselves," "Think about it for a moment"), but generally, it's the crisp professionalism one expects.

The preview copy of the documentary supplied by ABC News had many scenes showing nudity, but an ABC spokesman said these will be electronically altered for domestic consumption, because here in oh-so-sexually-sophisticated America, we only allow bare breasts and such on cable channels.

There was no word on whether another image would be doctored, that of a longhaired hippie who stands behind Koppel as he talks on a Leningrad street and flips the camera an obscene gesture. Ah, those lucky Russians -- becoming more like us every day.