WASHINGTON — With abortion and guns already on the agenda, the conservative-dominated Supreme Court is considering adding a third blockbuster issue — whether to ban consideration of race in college admissions.The justices on Monday put off a decision about whether they will hear an appeal claiming that Harvard discriminates against Asian American applicants, in a case that could have nationwide repercussions. The court asked the Justice Department to weigh in on the case, a process that typically takes several months.“It …