WHO is this bearded imposter claiming to be Elvis Costello?Could this grizzly dude in wire rims be the same trendsetter who, sidestepping the spiked hairdos of the punks, scrubbed his face, slicked back his hair, slipped on his thick plastic glasses, and glamorized the nerd back in the early '80s? If his exterior has changed, don't worry: The witty, scathing English singer's new album, "Mighty Like a Rose," is both cutting and sweet. From the pretty, melodic first track (released as a single), "The Other Side of Summer," to the merry-go-round sound of the adorable "Georgie's Rival," to the slow, haunting "Broken," Costello's album resembles thorny roses: Bursts of fragrant sounds atop the sharp, barbing attacks on hypocrisy, pop culture, and modern love. "Rose" is Costello's best album yet in his 15-year, 13-album career; but it is tempting to make that judgment each time he puts out a new album. His last one, "Spike," proved Costello could do more than write perfect pop songs like "Veronica." He could write mellow jazz and political ballads like the one that criticized the politics of Margaret Thatcher for kissing babies in public and slashing welfare programs behind closed doors. Costello has toned down his politics in this album, aiming instead at the hypocrisy of one of pop-music's heroes, the Beatles's John Lennon. "Wasn't it a millionaire who sang 'Imagine No Possessions? Costello asks in "The Other Side of Summer." (Rankling a few fans, Costello said in a New York Times interview that he thought "Imagine" was one of Lennon's worst songs.) In the same single, Costello pierces the pressures of pop culture and the immaturity of the TV-age: "The pale pathetic promises that everybody swallows/A teenage girl is crying 'cos she don't look like a million dollars/So help her if you can/'Cos she don't seem to have the attention span...." Love, Costello's main theme, is not only mighty like a rose, but short-seasoned. In the sticky-sweet "So Like Candy," (co-written with former Beatle Paul McCartney), a young man pines for the girl who left him. Staring at her photo, he misses her bad habits (and perhaps misses the irony): "Here lie the records that she scratched/And on the sleeve I find a note attached.../She couldn't say 'goodbye,' but, 'I admire your taste. (Costello sings the word "scratched" with the proper onomatopoeic harshness of a roughed-up album.) But when love finally works out, and the lovers mature (to the age where Costello's oldest fans are, in their 30s and 40s), Costello paints it fragile and almost morose. In the final track, "Couldn't Call It Unexpected No. 4," he sings: "Well you can laugh at this sentimental story/But in time you'll have to make amends/The sudden chills where lovers doubt their immortality/As the clods cover the sky the evening ends/... So toll the bell/Or rock the cradle/Please don't let me fear anything I cannot explain/I can't believe I'll never believe in anything again." Costello's new album shows that this musician, by any other haircut, still sounds sweet.