POP MUSIC REVIEW : Righteous Brothers Keep Their Melodies Unchained : They still generate the vocal excitement that made them a sensation a quarter-century ago.

“She’s my mashed potato baby / Little Latin Lupe Lu.”

It’s near impossible to say why, but that Bill Medley lyric to the 1963 hit “Little Latin Lupe Lu” always struck me as one of the most brilliant lines in rock. You surely won’t find rock critics confusing it with Faulkner, but in some ways, this line, and the spirit of the song it’s from, is what rock is all about.

That, along with Little Richard’s ululant ravings, the muffled two-chord guitar solo on the Beach Boys’ “Don’t Worry Baby” and the bare logic of the lyric “I needed money ‘cause I had none” in Sonny Curtis’ “I Fought the Law,” expresses a freedom that “serious” rock can only talk about.

There’s an abandon, a flippancy, at work, a notion that rock is a whole other world that need refer only to itself. While both major U.S. political parties tried to claim Bruce Springsteen’s lyrics as their own a couple of election years back, even at his most whacked-out you never would have caught Ronald Reagan dropping “She’s my mashed potato baby” into a State of the Union address.

“Little Latin Lupe Lu”--which, by the way, introduced the word groovy four years before the Summer of Love arrived--was part of the Righteous Brothers’ show at the Hop on Monday. And if--in this age of soundtrack ballads--it is unlikely Medley will ever write such a song again, he and partner Bobby Hatfield do still sing it with a remarkable abandon.

In large part their performance Monday mirrored the show captured on their mid-’60s live album “One for the Road”-- even down to an oldies medley that included “Cherry Pie,” “We Belong Together” and “Earth Angel”--and in the interim they must have performed their hits literally thousands of times. Yet the Orange County duo, both of whom turned 50 this year, still generate the vocal excitement that made them a sensation at county clubs and military bases a quarter-century ago.

Reportedly it was at one of their military-club gigs that a black fan exclaimed, “That’s righteous, brother!” providing them with their name. It was an apt moniker, for few other white singers, particularly of that era, were as capable at capturing the black feel and sound in their music. That mastery was evident Monday on a medley of “Hold On, I’m Comin’ ” and “Soul Man.” While those songs have been subjected to countless shuck-and-jive renditions over the years, Hatfield and Medley tore the songs up in a way that hasn’t been heard since Sam and Dave split up.

When fellow Phil Spector recording artist Tina Turner sang “River Deep, Mountain High” she well could have been referring to Medley and Hatfield. With a vocal geography made up of Medley’s incredibly deep valleys and Hatfield’s high tenor and falsetto peaks, it’s a wonder the two voices blend as well as they do.

Their singing is nearly as forceful as it was in the past, and both voices, particularly Medley’s grainy baritone, have gained in character. On “(You’re My) Soul and Inspiration,” the show’s second song, both singers let out with some devastatingly emotive shouts after the song’s spoken refrain. Even Hatfield’s vocal tour de force, the “Unchained Melody” recently revived by its inclusion in the movie “Ghost,” was strongly rendered, with him fudging only a bit on the highest notes.

The pair also tackled “Hung on You” (The now-obscure song was originally intended as the A-side of “Unchained Melody”), “Georgia on My Mind,” Medley’s own movie hit “(I’ve Had) The Time of My Life,” “You’ve Lost That Lovin’ Feeling” and “Brown-Eyed Woman. “My Babe” featured a hot extended solo from guitarist Barry Rillera, who has been with the pair practically since they were righteous embryos. The only songs in their set that didn’t hold up were their 1974 hit “Rock and Roll Heaven” and Bob Seger’s “Old Time Rock and Roll,” both of which could only benefit from incineration.