Prime Minister John Howard of Australia evidently is worried that the United States has once again turned to isolationism, and he has cautioned Americans and other nations to be wary.

In a toast at a state dinner in the White House last month, Howard said he had a single message for Americans: "The world continues to need America, and the world will be a better place for the involvement and the commitment of the people of the United States of America in the years that lie ahead."

With a nod toward anti-American outbursts around the world, he said: "Those foolish enough to suggest that America should have a lesser role in the affairs of the world should pause and think whether they really mean what they say, because a world without a dedicated, involved America will be a lesser world, a less-safe world, a more precarious world."

Moving to Chicago, Howard was even more pointed in remarks to the Council on Foreign Relations: "It is vital, for America's interests as much as those of the rest of the world, that America not retreat."

Addressing politicians who attack the United States, the Australian leader said: "To the voices of anti-Americanism around the world, to those who shout 'Yankee Go Home,' let me offer some quiet advice: Be careful what you wish for."

The consequences of an American slide into isolationism, coupled with ignoring Howard's advice, could be substantial. In the U.S. elections in November, the war in Iraq is sure to be an issue. Will the debate go into the deeper question of whether the U.S. should continue to have alliances and deploy forces abroad?

U.S. relations with allies in Asia, not only Australia, may be affected. Political leaders and defense officials in Taiwan privately asked this correspondent a few weeks ago whether the U.S. would keep its commitments to help repel a Chinese attack. Japanese expressed the same anxiety but with less concern.

The combination of American isolationism and virulent South Korean anti-Americanism could hasten the demise of the U.S. alliance with Seoul and a reduction of U.S. forces in South Korea, and possibly their withdrawal.

Then there is the question of how a perception of American isolationism may affect negotiations with North Korea and Iran over nuclear weapons, possibly encouraging Pyongyang and Tehran to take tougher bargaining positions. China, with whom relations are often fragile, may be emboldened if Beijing believes that U.S. engagement abroad is declining.

Much of the revival of what a diplomat from the Asia-Pacific region called a "recurring theme" in U.S. history seems to have been caused by an American reaction to widespread anti-Americanism abroad. The Pew Research Center in Washington asserted last year: "Anti-Americanism is deeper and broader now than at any time in modern history."

At the same time, Pew researchers found that more Americans believed that the United States "should mind its own business internationally and let other countries get along the best they can on their own." The researchers found that 42 percent of Americans felt this way, up from 30 percent only three years earlier.

President Bush has recognized the surge of isolationism and cautioned against it. In his State of the Union message in January, he said: "In a complex and challenging time, the road of isolationism and protectionism may seem broad and inviting — yet it ends in danger and decline."

Dick Morris, onetime adviser to former President Clinton and a shrewd political analyst, wrote in April that "Americans are again turning inward and rejecting involvement with the rest of the world." In Front Page magazine on the Internet, Morris said that frustration over the prolonged war in Iraq had generated among Americans "this feeling of wanting the rest of the world to go away."

Secretary of Defense Donald Rumsfeld warned Asia-Pacific defense leaders gathered in Singapore early this month: "In past decades, some of the people in the United States have questioned whether America should be engaged in the world. We've had strains of isolationism in our country, which we are all aware of."

Summing up the options for America and the world, Secretary of State Condoleeza Rice said in a speech on Wednesday: "Here, ladies and gentlemen, is the choice before our country, before us as Americans," she said. "Will we lead in the world or will we withdraw? Will we rise to the challenges of our time or will we shrink from them?"

Richard Halloran is a Honolulu-based journalist and former New York Times correspondent in Asia. His column appears Sunday in the Focus section.