BANGKOK — The prime minister of Malaysia, Abdullah Ahmad Badawi, said on Wednesday that he would step down in March 2009. His departure would pave the way for his chosen successor to take control of a governing party that appears to be losing its grip after five decades in power.

Mr. Abdullah, who was widely criticized inside and outside his party for a languid leadership style, has been prime minister for five years. After leading his party to near defeat in elections last March, the poorest results for the governing coalition in its history, calls for his resignation have steadily mounted amid simmering ethnic tensions in Malaysia and discontent over rising prices.

The accession to the top job by Mr. Abdullah’s chosen successor, Deputy Prime Minister Najib Razak, is not a sure thing. Mr. Najib must first win party elections set for March.

In making his announcement on Wednesday, Mr. Abdullah was surprisingly noncommittal about Mr. Najib’s prospects.

“At some point, I will have to hand over to my successor,” Mr. Abdullah said. Once Mr. Najib wins the party elections, “then we can discuss,” he said.

The governing party, the United Malays National Organization, also faces a resurgent opposition led by Anwar Ibrahim, who remains a powerful threat even though he has not delivered on recent promises to unseat the government.

Although Mr. Abdullah’s announcement removes one layer of uncertainty for the governing party, analysts say Mr. Najib will find it difficult to reunite the party and assert control.

“Najib faces a very difficult terrain,” said Bridget Welsh, a specialist in Malaysian politics at the Johns Hopkins University School of Advanced International Studies in Washington.

In a survey carried out in September by the Merdeka Center, a nonpartisan polling institute, 44 percent of Malaysian respondents said they believed Mr. Najib would not make a good prime minister, while 39 percent had a favorable opinion of him.

Ms. Welsh said that Mr. Najib, whose father was Malaysia’s second prime minister and whose uncle was its third, has been in Parliament for more than three decades, since the death of his father. He has a record of favoring authoritarian measures and continuing the policy, begun by his father in the 1970s, of preferential treatment for the country’s Malay ethnic majority. He is not popular among the large Indian and Chinese minorities in the country.

One major hurdle for Mr. Najib will be persuading voters that he had no role in the 2006 murder of a Mongolian woman whose body was destroyed using military-grade explosives in a patch of jungle outside Kuala Lumpur, the capital. Two of his longtime assistants and two Malaysian commandos are currently on trial in connection with the woman’s death.