CEDAR RAPIDS, IOWA -- When the abortion drama reopened in Iowa this year, the cast was familiar, but all the roles seemed to have been reversed.

The aggressive, outspoken leaders of the antiabortion movement here have been accustomed to the spotlight. After helping defeat two liberal Democratic senators -- Dick Clark in 1978 and John Culver in 1980 -- they have been cited and studied as models of grass-roots single-issue expertise. But now, on a stage reshaped by recent Supreme Court decisions, they are presenting themselves in a different manner: quieter, less obsessive on the abortion issue, equally interested in other questions.

Republican Rep. Thomas J. Tauke, a veteran antiabortion leader who is challenging incumbent Democratic Sen. Tom Harkin, is counting heavily on the grass-roots assistance of the Iowa Right to Life Committee, which is as well organized as ever. But when it comes to the 1990 race, Tauke said, "abortion is disappearing as an issue." And his communications director, Allen Finch, insisted: "Abortion just doesn't come up."

Leaders at the local level offer a similar view. "I really don't like to see the hype being placed on abortion," said Marlys Popma, president of the Iowa Right to Life Committee. "I think it's important, but not a litmus test, not a referendum on abortion. . . . I don't believe we should paint whole elections with this issue."

Did that mean Popma might support candidates who differed with her on the abortion question if they agreed on other issues? Not quite. "I will talk every other issue with you," she said. "But if you give me someone who doesn't value life, you've lost my vote."

This year the aggressive role that once belonged to the antiabortion leaders is being played by the National Abortion Rights Action League (NARAL), which is mounting what is known as an "independent expenditure" campaign on behalf of Harkin while also pushing Democratic House Speaker Donald Avenson in his bid to unseat Republican Gov. Terry E. Branstad. NARAL, which took some credit for the victories last year of abortion-rights governors in Virginia and New Jersey and for Avenson's primary win over antiabortion Democratic Attorney General Tom Miller, targeted Iowa as its main arena this fall and may spend several hundred thousand dollars here by November.

"For certain, abortion is the most important issue," said Shelley Bain, an Iowa native and the executive director of NARAL's state affiliate, whose year-old Des Moines office staff also includes a full-time field organizer and volunteer coordinator.

While the political arm of the national abortion-rights lobby is making its first concerted effort in an Iowa Senate race, the emphasis on abortion marks a clear change for the group's favorite candidate. When he won election six years ago, Harkin played down the issue, even making a point of returning a NARAL contribution.

Washington pollster and political consultant Harrison Hickman, who has conducted surveys for NARAL in Iowa and several other states, said the importance of the abortion issue is sometimes indirect: Once voters key on a candidate's abortion position, they often take a closer look at other issues on which they agree, strengthening the voter-candidate compact.

That process, Hickman said, might explain why the Iowa Right to Life Committee, which was once so assertive, now seems hesitant to place its issue in the forefront of the Senate and gubernatorial campaigns: Tauke and Branstad have a better chance this year running as moderates than as staunch antiabortionists.

"There's an irony to their attempts to limit the importance of the issue," Hickman said. "It's a testament to how much the world has changed."

In the ideological spectrum of the 50 states, Iowa falls somewhere near the middle on abortion, with Oregon on the abortion-rights end and Louisiana on the antiabortion end. Public opinion polls on the issue are tricky: Answers vary widely depending on the wording of the questions. But most polls show that somewhere between 58 and 69 percent of Iowans believe women should have the basic right to choose whether to have abortions.

The numbers are higher in cases of rape, incest and when the life of the mother is endangered by the pregnancy, according to independent polls. But a survey conducted for the Iowa Right to Life Committee by Beacon Associates showed a majority of Iowans thought it should be illegal to have an abortion if the fetus is not the sex desired by its parents, the woman cannot afford the child, the father is unwilling to raise the child or the procedure is used as a method of birth control. The Beacon poll also said that 88 percent of respondents thought minors should have parental consent before having an abortion.

The disparate numbers make it possible for both sides to stake a claim to what they like to call the "mainstream" public position. NARAL's Bain, noting that Tauke approves of abortions only to save the life of the mother, said that he is "way out of the mainstream." But Popma said Harkin "is really out of the mainstream" for supporting abortion rights with few restrictions. Harkin does support parental consent requirements.

With abortion rights supporter Harkin leading Tauke by between 10 and 15 points in the polls in the Senate race, and antiabortion Branstad leading Avenson by a similar margin in the gubernatorial contest, it is obvious that most Iowans are not single-issue voters. But the ability of candidates to target and get single-issue voters to the polls on election day still might be crucial.

According to Hickman's study of Iowa voters, the percentage of abortion rights voters who say that will be the most important issue has increased dramatically over the last decade, from 8 percent in 1980 to 18 percent this year, while the portion of antiabortion voters who use that as the decisive issue has remained steady at 10 percent. Antiabortionist Popma cited similar figures for her side, saying she could always count on "a solid 7 to 11 percent" who will "vote solely for us on this issue."

But if the political landscape is changing in Iowa and the abortion rights movement is gaining organizational strength, it was not readily apparent Wednesday night when Tauke and Harkin met for a 60-minute televised debate on abortion. While the two candidates faced off in a Cedar Rapids studio, advocates on both sides of the abortion issue gathered for big-screen debate-watching parties at hotels on opposite ends of town. The gathering sponsored by NARAL drew 18 people. The one held by Iowa Right to Life brought in more than 150.

The abortion-rights gathering, while small, included at least one person of the type Harkin and NARAL are counting on to make the difference this year. Sue Humphrey, a nurse, said she was a registered Republican who had voted for Tauke in his last five congressional races because she considered him a moderate and she was not too concerned about the abortion issue.

"The Webster decision last year turned me around," she said of the Supreme Court ruling in Webster v. Reproductive Health Services, a case from Missouri in which the court allowed states to consider new restrictions on abortion. "I am pro-choice, and I can no longer support any anti-choice candidate, ever, with my vote or financially."

Across town, the mood at the Iowa Right to Life gathering was effusive. People jeered and laughed when Harkin, in the same sentence, called himself both "pro-choice" and "pro-life."

"Oh, c'mon! No way! You can't be both," said Margaret Spear, 68, leader of Linn County Lutherans for Life.

Mark Boddicker, 44, a soybean farmer from Walker who drove 30 miles to watch the debate at the antiabortion gathering, led the cheers when Tauke spoke out for what he called "the rights of the unborn." Boddicker said he was especially glad that Tauke opposed abortion for rape victims. "If Roe v. Wade is overturned," Boddicker said, "we'll end up having 90 percent abortion on demand anyway because women will claim they were raped."

Entering the debate, Tauke said his objective was to handle the issue in a straightforward manner. If he stated his position without equivocation, he said, voters would accept it and move on to other issues. But Hickman, the NARAL pollster, said Tauke's strategy might backfire.

"Tauke may think he's getting it out of the way," Hickman said. "But the other way of thinking about it is: He'll lose voters early and not get them back."