President Reagan billed her as the "feature act" in the Reagan road show, and today First Lady Nancy Reagan brought her campaign against drug and alcohol abuse to the Iowa heartlands.

"While the cities and suburbs get the most attention," she told an audience of youth and parents in Ames, "rural areas are increasingly getting caught up in the drug culture. Really, no area is safe from the threat."

She was the second Reagan to show up in the Hawkeye State this week, and she laughed when she said, "I hope you don't get tired of them." The president was here on a fence-mending trip Monday to reassure farmers and other supporters that he hadn't forgotten their election-time help.

Mrs. Reagan was in Iowa to inspect drug abuse prevention and treatment programs in several cities and to see Gov. Robert D. Ray, with whom she had a working lunch. She also met with 4-year-old Katie Beckett at Cedar Rapids Airport, the disabled child cited last winter by President Reagan as a victim of federal red tape. Her parents could not afford in-home medical treatment and were eligible to receive Medicaid benefits only if Katie remained hospitalized--as she had been since she was four months old--with viral encephalitis. After the president mentioned this in a news conference, federal officials announced they would make an exception to the rules so Katie could be treated at home and still receive benefits.

Mrs. Reagan called the child's mother, Julie Beckett, Tuesday evening to set up today's meeting. The first lady brought along a large, stuffed, floppy eared rabbit to give to the child and then asked her, "What are you going to name my friend here? I got kind of attached to him on the plane."

Said Julie Beckett, "We named her doll Nancy. I hope you don't mind."

Earlier in the afternoon, Mrs. Reagan was a guest on a call-in show on radio station WHO in Des Moines, where her husband had once been a sports broadcaster. Coincidentally, the station's frequency is the same as that given Radio Marti, the station the Reagan administration established to reach Cuba. WHO is seeking congressional relief from having the same frequency because of fear that Cuba will jam the station and wipe out WHO's nighttime service.

Today, the call-in show's host, Jon London, told listeners that the only topic "we'll be able to take your calls on" would be drug and alcohol abuse. Sheila Tate, Mrs. Reagan's press secretary, said later "that was our wish." She added that since the entire day was devoted to drugs, she felt it was the only way to handle the program.

London reminded Mrs. Reagan that had she walked in the door some years back, she might have found her husband at the mike. How did she feel about coming to WHO, he asked?

"Disappointed," the first lady said. "I thought this was the same building, but it isn't. I have the microphone he used to use."

"Yes, we gave it to him," London said.

"It's strange," said the first lady. "I feel if I looked over my shoulder, he'd be there."

Gary Riedmann, director of the Iowa State Substance Abuse Program, and Dr. Carlton Turner, director of the White House Drug Abuse Policy Office, joined Mrs. Reagan on the show. Riedmann's office is losing half a million dollars of federal funds in the coming year.

One caller asked Mrs. Reagan how she suggested these drug programs she was supporting be financed. "I don't think financing is the real problem," Mrs. Reagan said. "Alcoholics Anonymous is extremely successful, and it's not federally financed. I never have thought that money is the answer."

Mrs. Reagan said she is a "big believer" in parents' groups and "since we started on this they've grown from 1,000 to 3,000." She told of the effect they are having in closing down paraphernalia shops, in changing laws and in alerting schools to the problem.

To another caller asking what advice she would give a parent whose child was using drugs, the first lady said, "Keep the lines of communication open, be more knowledgeable about drugs and be aware of changes in your child's personality."

Tate said later that Mrs. Reagan was not taking credit for the increasing number of parents' groups. "As she said herself, it's a grass-roots effort that is starting up on its own," Tate said.

But she said that Mrs. Reagan has had a lot to do with helping "spread the word."

Carlton Turner said she did "a wonderful job" on the call-in show. "I didn't coach her at all. She handled things very nicely. In fact, I needed coaching from her."

In Ames, a small band of sign-carrying protesters calling themselves the Ames Peace Network, accompanied by another group seeking legalization of marijuana, NORML, met Mrs. Reagan as she arrived at the Welch Junior High School. She was there to tour a display of programs offered under an umbrella group called Youth and Shelter Services.

The protesters carried signs bearing such slogans as "Marie Antoinette had it coming." Another, held by a woman wearing a long gown and carrying a champagne glass, read "Cheese for the poor, champagne for the rich."

Inside the school, wearing a red and white three-piece Adolfo suit and red shoes, the first lady sampled hot dogs and sipped a Pepsi sold by the group to raise money to send about 50 children to the International Meeting of Recovering Chemically Dependent Youth in New York next month.

The agency also offered strawberry rhubarb pie, which, Mrs. Reagan said, "sounds as wholesome as Ames itself."

"But even in rural areas, drugs and alcohol are growing problems. There's just no place safe," she said, calling drug and alcohol abuse "the most democratic of all the problems we have."

Mrs. Reagan said programs like Youth and Shelter Services were providing essential aid to young abusers of the substances.

"I'm so proud of these kids, I could just pop," she said. "If I lived here, I would be out there throwing kisses at the buses" as the youths leave for New York.

George Bellitsos, director of the program, said Mrs. Reagan's visit helped raise enough money to send 10 more people to the New York seminar.

Later, when she arrived at the University of Iowa in Iowa City, a small band of highly vocal protesters was there to meet her as she got out of her car. "Nice dress Nancy--10,000 bucks?" yelled one youth. Another called, "How would you like to eat garbage?" At the university, she observed a series of skits and took part in a group discussion that was part of a summer school training program for professionals and counselors in substance abuse.

At one point they drew her into something called a "circle of support," to illustrate the need for mutual involvement on all levels, in which about 20 persons crouched as if to sit on the lap of the person behind. If one fell, the whole circle would fall.

Mrs. Reagan took it in good stride and asked the man in front of her how much he weighed. He replied, "About 175 pounds." She said "okay." When Mrs. Reagan left, she walked grim-faced past the same group of protesters who had booed her arrival. They held signs that read "Your husband's policies are driving us to substance abuse" and "Recession breeds depression."

Later, aboard her Air Force jet en route to Dallas, she and her projects aide, Ann Wrobleski, demonstrated to others on her staff how the circle was done. "See," the first lady said, "you don't feel anyone's weight."

Mrs. Reagan's Iowa visit had been heralded by the president when he told corn growers in Des Moines that he was just the warm-up for the real star in the family. Recalling how vaudeville acts were scheduled, he said, "The feature act was always preceded by a lesser act, usually a trained animal act," he said. "Well, here I am."

Gov. Ray and his wife Billie were at the airport to meet the first lady when her plane arrived in Des Moines. Traveling with her were the wives of both of Iowa's senators, Barbara Grassley and Dee Jepsen. The White House said it was "just coincidental" that both Reagans visited Iowa in the same week. Barbara Bush also has been here recently, and her husband, the vice president, is due here soon.

Both Senate wives said reaction to the president's announcement that he has extended the current grain agreement for one year had been positive. "My husband's reaction was that it is the greatest farm speech he ever heard," said Dee Jepsen.

Barbara Grassley said she thought most people realized the president's economic program hasn't been "in place all that long."