LONDON — With just a week left in power, Prime Minister Theresa May used a valedictory speech on Wednesday to denounce the rancor, divisiveness and “absolutism” of politics both internationally and in Britain, where Brexit continues to tear apart her Conservative Party as it has since she took the job three years ago.

In a strong attack on populism and a defense of the postwar liberal order, Mrs. May was careful to mention neither her likely successor, the former Foreign Secretary Boris Johnson, nor President Trump, whose comments on four liberal, minority first-term congresswomen she criticized this week. By contrast, she singled out President Vladimir V. Putin of Russia for criticism by name.

Nonetheless, she called on the United States to accept the need for multilateral institutions, and warned against the “politics of winners and losers, of absolutes and of perpetual strife,” a concept, she said, “that threatens us all.”

A refusal to compromise, Mrs. May said, had coarsened public debate. “Some are losing the ability to disagree without demeaning the views of others,” she said, speaking to an invited audience at Chatham House.