SYDNEY, Nov. 24 — Prime Minister John Howard of Australia suffered a comprehensive defeat today, with a coalition led by his Liberal Party losing its majority in parliament.

After four terms in office, he will be replaced by Kevin Rudd, a Labor Party leader and former diplomat. Mr. Rudd, 50, campaigned on a platform of new leadership looking for new answers for new challenges. He has said his first acts as prime minister will include pushing for the ratification of the Kyoto climate agreement and to negotiate the withdrawal of Australian combat troops from Iraq.

The attempts by Mr. Howard’s coalition to stress their economic record failed to impress voters. The Australian economy has had 17 years of continuous growth, in latter years driven by Chinese demand for Australian iron ore and coal, and he had warned voters that a Labor victory would endanger the country’s future prosperity.

But despite the coalition campaign, there was little distance between the two parties on economic policy, and the defining characteristics came down to the personalities of the leaders and Labor’s promise to readdress broad concerns about the environment, health and education. Mr. Howard, 68, was running for a record fifth term in office, but many voters said they were ready for a change.