WASHINGTON — Standard & Poor’s removed the United States government from its list of risk-free borrowers for the first time on Friday night, a downgrade that is freighted with symbolic significance but carries few clear financial implications.

The company, one of three major agencies that offer advice to investors in debt securities, said it was cutting its rating of long-term federal debt to AA+, one notch below the top grade of AAA. It described the decision as a judgment about the nation’s leaders, writing that “the gulf between the political parties” had reduced its confidence in the government’s ability to manage its finances.

“The downgrade reflects our view that the effectiveness, stability, and predictability of American policymaking and political institutions have weakened at a time of ongoing fiscal and economic challenge,” the company said in a statement.

The Obama administration reacted with indignation, noting that the company had made a significant mathematical mistake in a document that it provided to the Treasury Department on Friday afternoon, overstating the federal debt by about $2 trillion.