Yearning for youth does Madonna no favours.

She has a stock answer for it now. American news anchor Cynthia McFadden recently questioned Madonna about the uncanny resemblance between her 1989 hit "Express Yourself" and Lady Gaga's "Born This Way". What did she think of the comparison - indeed, the general opinion sweeping the planet that Gaga has taken her place? Madge fixed her with a frosty glare. "I think it's . . . reductive." What do you mean? "Look it up." It must be tiresome, navigating your way through a silly media-fuelled catfight, but that's what they're saying: Gaga is Queen of Pop and Madonna, usurped, must be put out to grass.

Last week the first single from her new album MDNA, "Give Me All Your Luvin'" - a cheer-leader anthem pre-tooled for the No 1 slot, featuring hot girl-rappers MIA and Nicki Minaj - entered the UK charts at No 37 and fell away quickly, the lowest performance of any of her 75 singles since 1982. Madonna's made some odd choices in the past decade ever since that kiss with Britney Spears. Collaborations with younger artists seem under-confident, while the rush to incorporate new urban production values looked like a woman running to keep up. Then her directorial debut, W.E, became a cult phenomenon the moment the trailer hit YouTube - because it looked so awful. All this, from the toughest pop star and businesswoman the world has ever known?

Madonna, like Blackadder's Queenie, has the body of a weak and feeble woman and the heart and stomach of a concrete elephant. Her commercial and artistic decisions have generally been flawless. She was the first MTV star and exploited the video age with a kaleidoscopic rotation of new "selves", each one so expertly crafted we never wanted to know who the real person was. From Catholic ingénue to Mario Testino model, Erotica porn star to Eva Perón, Kabbalah-scented cowgirl to 1970s disco diva - these were much more than costume changes. Each persona took root for a couple of years; they were Madonna. In that respect she is unique - for that magical limbo she occupied between being and seeming.

You can't say the same for Gaga. Her platform is the two-hour stage show - she's a performance piece, mistress of the dressing-up box. We get commentary from her and warmth; she's empathetic towards her "little monsters" in the crowd and adrift in the world she's created, offering herself up in the service of "her art". You wouldn't want to hear Madonna talk about "her art" any more than you'd want Gaga to talk about her music. She is pure, first-generation pop - one of the 1980s machines, like Michael Jackson, whose vast live shows were just part of the job. The question is not whether she has been "replaced" by a younger model - but whether she's allowed to be a pop star at all aged 53.

This is the feeling stirred by MDNA, whose title embraces pop's transient nature (punning on the clubbers' drug du jour, it'll sound gloriously out of date in ten years' time). The first half of the songs were produced by French and Italian electro-house DJs, the other half given to the composer/producer William Orbit, who shaped Madonna's dazzling Ray Of Light album in 1998. Spoken word rings out on the opening track, "Girls Gone Wild", over a blasting rave backdrop: "girls say just wanna have some fun/get fired up like a smoking gun". "Gang Bang" is even more defiantly dumb ("I shot you dead/in the head") and on "Turn Up the Radio" ("I just want to get in my car") she sounds as young and daft as she did on "Holiday".

These songs are built for the dance floor but their determined superficiality is strangely alienating coming from the mouth of someone with such a terrific story to tell. You're never going to get a confessional from Madonna but there has been a humanity in some of her musical faces, and here it's found in the William Orbit tracks - "Masterpiece", from W.E (it won a Golden Globe) and "I'm A Sinner", which features the same sweet, psychedelic guitar he used on "Ray Of Light", its chorus gospel-infused, its lyrics all about saints. Orbit's analogue instruments make Madonna's voice more lustrous. She sounds appealingly eccentric around him too, cataloguing the woes of marriage on "Love Spent" ("Frankly if my name was Benjamin, we wouldn't be in the mess we're in.").

“Falling Free", the closing track, is a rather magical, bucolic meditation, bubbling away on a bed of strings and harp. "When I move a certain way, I feel an ache I've kept at bay . . ." She would do well to sing lines like that more often - it's one persona we've never been allowed to see. We're living in the age of the emotional pop star now and perhaps, in this respect, Madonna is behind the times.

None of the Orbit songs are up for singles so far - it's the chilly, adolescent dance-floor numbers instead. This is significant. Perhaps Madonna is fighting for something, after all. The point is, she doesn't need to.