WASHINGTON – A majority of the U.S. Supreme Court appeared poised yesterday to reverse or limit a line of precedents with roots — some more than a century old — that has allowed the government to ban corporate and union expenditures in election campaigns.

After an extraordinary 90 minutes of oral argument in Citizens United v. Federal Election Commission, it seemed likely the Court, swayed by arguments in favor of First Amendment rights for corporations, was ready to embark on a new course that critics say could unleash a flood of corporate wealth into elections that are already awash in more regulated kinds of campaign spending.