Broadway tuner “Legally Blonde” will shutter Oct. 19 after a run of just over 18 months.

Production, which has grossed $54.1 million on the Rialto so far, is coming off a strong summer that saw weekly sales boosted to the mid-$800,000 range by “Legally Blonde: The Search for Elle Woods,” an MTV reality competish that cast the show’s replacement star, Bailey Hanks.

However, the Rialto’s annual post-Labor Day downturn caused box office to fall to about $350,000. Last week, receipts tallied $432,876.

Decision to shutter — rather than hold out for the major bump in biz that comes over the Thanksgiving and Christmas frames — was prompted in large part by worries about a prolonged economic downturn.

“It’s scary out there,” said producer Hal Luftig. “If this were another year, we’d say, ‘Let’s weather this storm.’ ”

Show has not yet recouped its capitalization costs (reportedly between $9 million and $10 million), although future life for the tuner will continue to add coin to investors’ pockets.

The national tour, which Luftig said is booked two years out, launched this week. Plans are brewing for potential productions in London, Korea, Germany and China.

Although the TV series provided the most noticeable bump in sales, the skein marked the second time the production had paired with MTV, the youth-oriented network whose target demo matches that of “Blonde.”

Last year MTV broadcast a multi-camera, edited recording of the complete stage musical, an unusual move made with the intention of exposing the stage show to national auds.

Based on the 2001 MGM pic adapted from the novel by Amanda Brown, “Blonde” centers on sorority-girl-turned-law-student Elle Woods. Laurence O’Keefe and Nell Benjamin wrote the score, while “Blonde” screenwriter Heather Hach penned the book.

Helmed by Jerry Mitchell, “Blonde” tried out in San Francisco in early spring 2007 ahead of an April 29 opening last year in Gotham. Luftig, Fox Theatricals and Dori Berinstein produce in association with MGM Onstage, Darcie Denkert and Dean Stolber.

The show’s closing leaves a vacancy at the Palace Theater, the nearly 1800-seat venue owned by the Nederlander Org. Upcoming musicals looking for a Nederlander house this spring include “West Side Story” and “Guys and Dolls.”