WASHINGTON, Jan. 28 — President Bush will seek a big increase in the budget of the National Endowment for the Arts, the largest single source of support for the arts in the United States, administration officials said on Wednesday. The proposal is part of a turnaround for the agency, which was once fighting for its life, attacked by some Republicans as a threat to the nation's moral standards. Laura Bush plans to announce the request on Thursday, in remarks intended to show the administration's commitment to the arts, aides said. Administration officials, including White House budget experts, said that Mr....