After the frivolities of September - awkward "Oh, Kay!," aborning "Platinum" and delicious "Dolly" - heavy drama breaks out this week.

"Semmelweiss," now previewing, opens Monday at the Eisenhower. It is Howard Sackler's first play since his Pulitzer-winning "The Great White Hope." The story is of a Viennese doctor's quest into the causes of "childbed fever." Again, Sackler turns to history for his material, as he did in "Hope," inspired by black heavyweight Jack Johnson. Introduced last year by Buffalo's Studio Arena Theater, the play explores a mid-19th century conflict between compromise and conscience.

On Wednesday, the Folger Theater Group begins previews of Brian Clark's "Whose Life Is It Anyway?" to run Oct. 16 through Nov. 19. Into its seventh, admired London month, the play concerns a young sculptor and art teacher, permanently paralyzed from the neck down in an auto accident. His conflict is between doctors, lawyers and hospital computers and his own rationale to die a natural death with dignity.

On Friday evening, Arena Stage begins previews of Odon von Horvath's "Tales From the Vienna Woods," to open the following Wednesday for a run through Nov. 19. The production is David Chambers' first as Arena's producing director for the next two seasons while Zelda Fichandler has her long-delayed sabbatical. Introduced last year at Britain's National Theater in the first Horvath English translation, it is far from the romantic baroque its title suggests. The Strauss waltzes recur, ironically, during the play but also heard, more fittingly, is Chopin's funeral march.

There also is drama behind these three productions. Concurrently with the Folger, the Louisville Actors Theater is pressing a twin "first American production" of the Clark play. Concurrently with the Yale Rep. Arena is introducing "Tales, From the Vienna Woods," to America. As noted, Sackler's "Semmelweiss" was first performed at Buffalo's Studio Arena. All three, then, will have made their bows not in the traditional, commercial manner but through the nonprofit regional theaters.

Dramatic, too, behind the scenes, was an especially touchy summer for all those regional theaters. Besides the habitual "where's-the-money-going-to-come-from?" was the matter of the LORT contract.

LORT stands for the League of Resident Theaters, the relative of the League of New York Theaters. The latter represents commercial managements, while LORT refers to those professional resident companies across the land which rate special categories in Actors' Equity contracts.

Besides the raises all the theaters agreed their players had to have, there were controversial points which took from June into September to resolve. Negotiations were settled in the nick of time for LORT theaters to hold to their announced schedules.

One point concerned future rights of theaters and players to works they introduce prior to potential commercial productions. Ultimately, this aspect of future rights and roles was confined in the contract to "showcase" New York productions. The matter first arose 10 years ago with Arena's introductory production of "The Great White Hope." Now LORT theaters' credits and percentages, if any, rest on whatever term individual theaters manage to arrange in their initial contracts outside the scope of LORT. But such clauses will continue to be an Equity-LORT struggle.

Both Sackler and Clark are very much alive and work in England, so consider the errie career of Horvath, born in Hungary, at home in Austria and writing in German. He was killed in Paris in 1938 at the age of 36, author of 18 plays and considered the equal of his comtemporary, Bertold Brecht.

A week before his death, Horvath was told by an Amsterdam clairvoyant that he must go to Paris, that "the greatest event in your life awaits you there." So, to Paris he went. He made a June 1 appointment with film director Robert Siodmak. On his way, Horvath dropped in to see "Snow White and the Seven Dwarfs."

Lightning and thunder broke out when he left the theater and he joined a group sheltering under a chestnut tree opposite the Theater Marigny. An adjacent elm collapsed onto the chestnut tree, breaking off a branch which struck Horvath on the head and killed him instantly. No one else was hurt.

That "greatest event in you life" was in key with ironies which fascinated Horvath and which abound in "Tales From the Vienna Woods." His friends recalled how Horvath was haunted by his superstitions.

He had told an intimate, a year before his death, that he tried never to go out at the end of May or the beginning of June, yet he had made the June 1 appointment. In Arena's play there is a line: "Why is it most people are afraid of the darkness of the forest? Why aren't they afraid of walking down the street?" Champs Elysee is a small forest come to the city.

"The play itself is haunted," says director Chambers. "We scheduled it first of the season so we could have time to concentrate on it with no distractions. I've never had rehearsals in which everyone has been so physically involved. It's as though the playwright is there with us, listening, watching. At times we stop and say to each other: 'What does he mean here?' and we seem to listen.

"I didn't see the London production of Christopher Hampton's translation but as soon as I read its first 11 pages, I wanted to stage it. Had to stage it. It's about a very shadowy period of Austrian history, that between the end of the first World War and Hitler's takeover. Comparatively little has been written about that. Ever since studying the play, I've dug around for those who know the period or had some association with Horvath."

One authority Chambers found was USIA's Hans Holzapfel, an Austrian-born American who recalls seeing "Tales From the Vienna Woods" in his youth. "It was a period," says Holzapfel, "much like today, unsettled, anxious, with many of the same topics which obsess us now, economics, morality, decadence. Peter Handke, you know, has written an essay titled 'Horvath Is Better Than Brecht.'"

"The play will not be easy for our audiences," Chambers allows. "Seemingly unrelated, the scenes actually are very tightly knit. Horvath - and our actors - cannot do all the work. The audience must take part, fit the pieces together for themselves. Though there's humor here, ironic humor, I expect our audiences will be very intent and I expect, too, haunted, the way we have been during our rehearsals. This is a difficult, complex drama but we all have been wholly caught up in its undercurrents, implications and silences, the half-empty, apparently irrelevant remarks. What do they mean? Audiences will listen and, I think, understand."