When 64 million viewers saw Potsie—handsome Anson Williams—pin his sorority sweetheart, Jennifer—actress Lorrie Mahaffey—on Happy Days early this year, ABC was swamped with gushy fan letters. "One woman wrote, 'You acted like you really cared about him,' " recalls Mahaffey. She would like to take credit for a deft performance, but fact is, she and Williams had been courting for 18 months before the episode. Beyond the pinning stage now, they are getting married for real—before a slightly smaller audience—in November.

It could be a memorable autumn for them in another way, too. Mahaffey has her own role as aspiring singer Memphis O'Hara in NBC's new Friday night comedy hope, Who's Watching the Kids? Williams will return to Happy Days for a sixth season with his role beefed up.

For the newlyweds-to-be, "career" is very much a household word, but they insist, "We're not in competition—we're two completely different talents." The subject of children is in abeyance—"We'll cross that bridge later," says Mahaffey—but she's already made sure that if her show is a hit, her husband won't try to hold her back with sexist demands. "That's something I had to be sure about," she says. "If a man asked me to give up my career, he couldn't love me." Williams has worked too hard sharpening his own various talents—acting, singing, composing—to make such a request. In fact, he hasn't been above a little showbiz chicanery himself to get ahead. "When we met," recalls Happy Days co-producer Tom Miller, "he said he was 19. Three years later when we met again, he said he was 19. He's not above playing the game." (Williams, who portrays a college student on the show, is actually 29, three years younger than Henry Winkler.)

Adds Miller, "Anson keeps to himself on the set, but his mind is always clicking. It's not an uncalculating mind. He's very professionally prepared, and he knows his lines—he sees this as a stepping-stone."

To that end, he is quite capable of the grand overstatement—"No one has more adulation and fame than the cast of Happy Days." (Williams did receive one letter from a girl who "wanted me to make a baby. I said I couldn't afford it.") Now he's trying to tone down what Mahaffey gently calls a "high energy level" that in the past has rubbed some people the wrong way. "When I started out I was cocky mostly out of ignorance," says Anson. "Now I'm more humble."

Mahaffey agrees. "He's a street fighter, but he's mellowed out a lot. He just won't let people push him around, and in this town, that's necessary."

Williams grew up Anson William Heimlick in Burbank, the son of a technical illustrator who later ran an Orange Julius stand. (His father, Hal, now manages both Anson and Lorrie.) At age 20, Anson started going out on casting calls, at one point trying out for summer stock. "I waited in line with 300 people at the Los Angeles Masonic Temple," he remembers. "It wasn't El Slicko time. I saw my competition, heard great voices and had no confidence." The show's producer told him, "Your singing was terrible and your dancing worse. But Anson, you have something."

Earlier he worked as a shoe salesman and did occasional commercials while studying phys ed at Pierce Junior College. He won the Potsie role on the Happy Days pilot in an audition. Playing even third banana to Winkler and Ron Howard has obviously boosted his career, but Williams wants to diversify. He once despaired about his future in music—"I was writing terrible songs"—but as Potsie he has tried again, with much greater success. As a performer, he was the opening act for C&W star Tanya Tucker in 1976. "I was El Pop-O," he admits, "but I learned to respect country music." More recently he has played fairs and clubs across the country. He and partner Ron Rose have also composed 10 tunes for Happy Days.

Williams has vast ambitions. "I'd like to have a production company involved in developing and producing films, special things for television and a music end for writing songs, signing talent and creating a label," he says. Money isn't the only objective. "From Happy Days being a hit, it's become El Cusho time. I'm very appreciative. But it's not very satisfying."

Mahaffey is an "Army brat"—her father is a major general—who grew up on posts in Germany and the U.S. She sang four-part harmony with her three younger sisters in church and later joined a Virginia high school madrigal choir that performed at the Nixon White House and at Carnegie Hall. At 18, she began working in the Opryland variety shows in Nashville where Williams came to perform two years later. After dashing home to wash her hair, she introduced herself at a rehearsal, and, as he says, "We just both knew that was it."

Several months later she migrated to L.A. to be near him and to break out of her pure country mold. "I knocked on every door where there was live entertainment in Pasadena, Glendale and Burbank," she says. At one point she played a Holiday Inn with a rock band and, "after paying my manager," she remembers, "I had $70 left for two weeks." At Williams' suggestion, some Happy Days executives went to see Lorrie perform at a Ramada Inn near L.A. Airport. Six months later they hired her to appear in two segments.

Mahaffey claims that, as a relic of her peripatetic childhood, she's "driven crazy by anything that's too permanent. It would bother me career-wise if Who's Watching the Kids? packed down tomorrow, but I expect it." Marriage, she hastens to add, is an exception—"You look for stability in relationships."

Not that they don't argue. "I'm real Jewish about it," says Williams. "Yell! Scream! Get it out and then make up. We've argued in some strange places because I forget there are people around." (One set-to lasted three days. "My fault," Williams says. "I was so used to doing my thing that it took time to get used to a 50-50 relationship.")

One frequent sticking point is Mahaffey's habitual tardiness (a Southern legacy, she pleads). Another might someday be his mania for movies—on a recent Saturday the couple took in five of them—but they both realize there's a method to it. Says Williams: "Someday I may be directing a movie. The worst thing that could happen is to get to be a big shot—and not be prepared."