If love were all ...

Opposites attract.

To what extent that law of physics governs the world of romance is debatable, but it does help explain the reinvention of longtime rock ‘n’ roll rake Rod Stewart as an urbane purveyor of romantic sophistication.

On his first tour since delving into the Great American Songbook in two albums that have sold more than 4 million copies, Stewart had it both ways Monday at the Arrowhead Pond in Anaheim and scored some degree of success in each guise.

His 2 1/2-hour show, which also was due at Staples Center on Tuesday, began with a long set of his rock hits (heavy on the ‘80s) for which he dressed casually in black jeans and untucked shirts in pastels, accompanied by a hard-charging seven-piece band and three female singers.

After intermission, a seven-piece string section and percussionist supplemented the band for classic pop material from his “It Had to Be You ...” and “As Time Goes By ...” albums, showcasing a new and improved Rod, buttoned up in white tie and tails, replete with a red carnation in the lapel of his tux.

The costume change was the easy part. The tricky part for Stewart, particularly in concert, is pulling off the time travel required by his recently consummated love affair with songs of the pre-rock era of pop music.

It’s not simply the 180-degree shift in musical approach, a turn Stewart doesn’t fully make. His signature vocal rasp is ideal with the raw emotion of the late-’60s/early-’70s work that got him into the Rock and Roll Hall of Fame. He mined that period briefly Monday with “Reason to Believe,” “You Wear It Well” and “Ooh La La.”

The vocal nuance, shading and masterful phrasing that best suit the ‘30s and ‘40s songs aren’t Rowdy Rod’s forte. What those pop standards really require to succeed in his hands is a psychological time warp: from the morning after (the milieu that dominated Stewart’s energy and attention for some three decades) to the night before.

They also call for the rollback of a certain field of knowledge, in Stewart’s case the sexual and emotional freedom unleashed in the last half-century.

That makes it a bold step for him to present such genteel and circumspect songs as Herman Hupfeld’s “As Time Goes By” and Hoagy Carmichael and Ned Washington’s “The Nearness of You” or Rodgers & Hart’s subversively sexy “Bewitched, Bothered & Bewildered” after wrapping the show’s first half with “Stay With Me,” a rock masterwork of macho boorishness. (“Yes I’ll pay your cab fare home / You can even use my best cologne / Just don’t be here in the morning when I wake up.”)

It’s probably that contrast, more than his modest interpretive abilities, that explains the high level of public interest in his musical rebirth. Certainly there’s the curiosity factor in watching an eternal adolescent play dress-up in Daddy’s tux. But more than that, women who have long gushed over his love-’em-and-leave-’em sex appeal can now take heart in seeing a cad reformed. He becomes a confirmed scoundrel who at the far end of middle age has seen the folly of his loutish ways (on display in the show’s first half) and repented (the second).

That’s a critical component of Stewart’s immersion into the Great American Songbook because, strictly on musical terms, the homogeneity of the arrangements and the similarity of tempos (by and large lazy swing) combine to reduce most of those songs to a lowest-common-denominator appeal.

The tempo choice further lets Stewart avoid sustaining notes more than a beat or two, instead allowing him to lightly glide across the surface without ever slowing down to search for deeper levels of meaning. His easygoing renditions become perfect background music for baby boomers only casually familiar with (or interested in) the subtle complexities of songs of their parents’ generation.

All you really need with a song as lovingly crafted as Jerome Kern and Dorothy Fields’ “The Way You Look Tonight,” which earned Stewart the squeals of every woman he looked at while singing it Monday, is a vocalist who can carry a tune. A conventionally beautiful voice is no prerequisite, as anyone can tell you who has heard Louis Armstrong’s magnificent duets with Ella Fitzgerald on some of these same numbers.

“I love these songs,” he said at one point, “and I think it shows.”

In fact, Stewart’s genuine affection for the material is evident. Affection alone, however, isn’t enough to distinguish songs that have been recorded by many of the greatest pop singers the world has known. Ah, but is there anything more fascinating than watching such music work its charms to soothe one rocker’s formerly savage breast?