BOSTON — The Brattle Theater, a legendary repertory house in Harvard Square that gave birth to the Bogart cult in the ’50s, has fallen on hard times. The operators of the non-profit theater have launched what they are calling the “Preserve the Brattle Legacy Campaign.” Their goal is to raise $400,000 by the end of this year and another $100,000 by the end of next year. If the theater can not raise this year’s amount, it “will be forced to cease operations,” according to co-director Ned Hinkle.Several factors are hurting the theater. The availability of homevideo and now DVDs have long undercut the interest in going out to see older films. The Brattle tried to counterprogram by showcasing not only new films but highlight older films not out on DVD, but they are also up against the changing neighborhood. Much of what made Harvard Square a destination for college students and adults from around the Boston area — and not just from nearby Harvard — is no longer there. Locals have complained about national chains supplanting local businesses to no avail. The Brattle Film Foundation, which operates the theater, has made it clear that they need major investment to survive as ticket sales simply can’t support the operation on its own. If they can meet their goal over the next two or three months, it will allow them to pay off creditors, increase marketing and get on a solid footing. Then next year’s fund-raising would be to support what is being called a “strategic plan” for future development.