Billie Eilish and Taylor Swift Race for No. 1

A cold war between pop music titans — or at least their mobilizing fan bases and record labels — turned into a digital arms race this week as both Taylor Swift and Billie Eilish gunned for the No. 1 spot on next week’s Billboard album chart.

Swift, 34, has occupied the top of the Billboard 200 for the past four weeks with her blockbuster new album, “The Tortured Poets Department,” which has earned more than 3.6 million equivalent album sales so far (counting physical purchases, downloads and streams). But Eilish’s well-reviewed new album, “Hit Me Hard and Soft,” is challenging for No. 1 in its debut, as its 10 songs prove popular on streaming services like Spotify.

If only it were that simple.

Already, some impassioned followers of the two artists had been stoking a rivalry, dating back to comments Eilish made in March about “some of the biggest artists in the world” selling many vinyl versions of the same album, “which ups the sales and ups the numbers and gets them more money.”

The tactic, which Eilish called “wasteful” and damaging to the environment, has been widespread but used especially broadly — and effectively — by Swift. (Even before those comments, Eilish’s brother and main collaborator, Finneas, had once been heard on a hot mic joking about being “sued by Taylor Swift” after performing with an artist who had criticized her work.)

Eilish, 22, said later that she had not meant to single out any artist and added that she had participated in the practice, too. (Both artists’ work remains available in a variety of physical formats, though Eilish has stressed sustainability.)

Still, when Swift pre-empted the release of Eilish’s album last week with three special digital editions of “Tortured Poets,” available for 24 hours and including previously unheard “first-draft phone memo” demos, many saw the move as pointed. Especially online, where pop fan allegiance can be a blood sport, the matchup became one to watch.