Tuner “Once” leads the pack of nominations for Off Broadway’s Lucille Lortel Awards, with the musical nabbing seven nods while play “Tribes” scored six.Based on the 2006 indie film, “Once” preemed at New York Theater Workshop in an Off Broadway run, which qualified the show for Lortel consideration. Driven by strong response, the production recently opened on the Rialto, where it also earned largely glowing reviews. The wistful romance — with book by Enda Walsh and music by Glen Hansard and Marketa Irglova — scored nods for tuner, director (John Tiffany), choreographer (Steve Hoggett) and actress (Cristin Milioti), as well as a trio of design noms. Although no legit award serves as a truly reliable prognosticator of the Tony Awards, the Lortel haul might be a bellwether for the Broadway-centric Tony noms, unveiled in May. Among the thesps to score Lortel nods are Carey Mulligan, tapped as a lead actress for her perf in Atlantic Theater Company’s “Through a Glass Darkly,” and Hamish Linklater (Broadway’s “Seminar”), who gets the nom for his stint in the Classic Stage Company production of “The School for Lies.” Mare Winningham, in the running for featured actress, is among the nominations to be scored by “Tribes,” along with fellow cast members Russell Harvard and Jeff Perry. The American production of a well-received Brit play, Nina Raine’s “Tribes” also snagged noms for director (David Cromer) plus a pair for design. Director Sam Gold is in competition with himself in the helming category, scoring nods for current Playwrights Horizons offering “The Big Meal” (also on the list for play) as well as the Roundabout Theater Company’s revival candidate, “Look Back in Anger.” Created by the Off Broadway League, the Lortels will handed out May 6 in a ceremony at New York U.’s Skirball Center.