Everything about the new Backstreet Boys album, "Black & Blue," was poised for greatness. In what is turning into another banner year for the music business, the Backstreet Boys chose to release their album last week so it would be on record- store display racks on one of the biggest shopping weekends of the year.

The band's label, Jive, sent six million copies of "Black & Blue" to stores. Not only did this earn the album a multi-platinum award from the Recording Industry Association of America before a single copy had been sold, but it is also one of the largest initial shipments of a record.

The band also teamed up with Burger King for a summer promotional blitz; had a weekend of MTV programming to promote the album; put on a 100-hour promotional tour of the world, stopping for news conferences at landmarks in a half-dozen countries; and further greased the wheels of commerce by broadcasting a live performance the day the album was released throughout more than 1,000 Wal-Marts, which, in many rural areas, are the only convenient places teenagers can go to buy CD's.

With an album set up so perfectly, all eyes in the music industry turned to Soundscan when the music-sales tracking company released its weekly figures yesterday. Although the music industry likes to think that it has the teenage market sewed up and figured out, it is really at the mercy of the vagaries of youth, taste and whim. In 1999 the Backstreet Boys set a first-week sales record when 1.1 million copies of their "Millennium" album were sold; but last March 'N Sync decimated its rivals when 2.4 million copies of "No Strings Attached" sailed out of stores the week it went on sale. Before the release of "Black & Blue" some industry executives had predicted that the album would edge past 'N Sync's high-water mark.

The numbers came in yesterday, and the album sold 1.6 million copies, making it the third-highest in first- week sales of a CD, after Eminem, since Soundscan started tracking the data in 1991. It also makes the Backstreet Boys the first band in this period to break the million mark for first-week sales with two albums.

But at the same time many in the business are disappointed with the band's performance (or, for teen-pop cynics, secretly joyous). They wonder where the 800,000 additional fans who snapped up "No Strings Attached" went. Some record executives are wondering if teen-pop fans are aging out of the market as they mature and, in some cases, enter college. Looking ahead, music-industry analysts said that though overall numbers for music sales were strong so far this year, that was largely so because of the first quarter of 2000 (thanks again to 'N Sync) and that since March sales have been slipping each month.

Some said they were expecting the downturn in the stock market to trickle down to the disposable income of teenagers, curtailing the extraordinary purchasing power that has been changing the way mass entertainment is created, distributed and marketed.

For some, "Black & Blue" is the twilight of teen pop, the last blockbuster pop record of the genre, precipitating a downhill slide. For others, however, that is just wishful thinking. "It's weird to sit there and think that 1.6 million in the U.S. is a failure," said Tom Calderone, senior vice president for music and talent at MTV. I think it's an amazing feat because the Backstreet Boys beat their own record and they drove a ton of sales in the first week. I think the reason why people are saying it's the twilight of teen pop is because the genre was so loud when it came on the scene in 1999, and now it's part of the fabric. But it's just as strong."

The pillars of its strength, however, may be changing. With the Backstreet Boys now writing a few of their own songs, breaking hearts by marrying (two-fifths of the band so far) and edging toward a more mature sound to court an older audience, the upstarts that the record industry has had plenty of time to develop and market are flooding in. As anyone who has monitored the changing tastes on display on the MTV program "Total Request Live" can attest, the army of overseas teenage acts has strengthened its invasion, with the English boy-band BBMak and the black Irish singer Samantha Mumba moving in on the 'N Sync and Britney Spears audiences, respectively.

A new crop of American acts is sprouting on the pop singles charts, including the Canadian boy band Souldecision, the teen singer Mikaila, the Puff Daddy female group Dream, and a slightly older contender, the former beauty queen Debelah Morgan. But with the Backstreet Boys and Ms. Spears having raised the bar so high for teenage pop in the boom years of the economy, can teenage pop sustain itself as its stars age and the nation undergoes a political and economic transition?

"Overall, history has shown that when there are changes in G.D.P. or income, purchases like music decline," said Michael Nathanson, a music industry analyst at the brokerage firm Sanford C. Bernstein. "But that's a broad statement."

He said that fan attachments to these bands are in most cases too obsessive to be seriously affected if the economy dips. "There's probably a little hopefulness and wishful thinking that believes that teeny-bopper pop is going to go away," he said. "But I don't think it's going to happen yet."