By now we have all heard the grim punchlines about Ray Charles getting searched by airport securiry. But there is a less-publicized problem with the post-Sept. 11 atmosphere: an immigration clampdown that has caused paralyzing visa delays for an array of international performing artists.Well-established singers, ballet dancers and classical musicians from China, India and many other countries have been prevented from performing due to a months-long visa process that used to take 15 days. Cancellations have hit venues large and small and the hassles are starting to add up. These are not anonymous people making their first trip across the U.S. border. They are esteemed artists who have criss-crossed the globe, for decades in many cases. Tighter immigration policy should certainly be a goal of the White House’s war on terror. It arguably could have kept some of the Sept. 11 hijackers out of our country. We support the efforts of nonprofit groups and a bipartisan coalition of U.S. senators to ease not only the delays but also the onerous fees now attached to “expediting” visas. A sense of isolationism should not extend to the performing arts.