Thailand's Prime Minister Prayuth Chan-ocha is among the Southeast Asian heads of state invited to a summit in California later this month. (Athit Perawongmetha/Reuters)

PRESIDENT OBAMA has invited 10 heads of state from the Association of Southeast Asian Nations (ASEAN) to an unprecedented summit in California later this month — the first between ASEAN and the United States to be held on American soil. Mr. Obama’s aims are to advance his strategy of “rebalancing” U.S. foreign policy toward Asia and (though this is largely unspoken) to counter China and the clout it increasingly exerts over its smaller Asian neighbors.

While the purposes are worthy, the result of Mr. Obama’s initiative will be an unseemly parade of dictators at the Sunnylands resort, including a few long treated as too toxic to be granted the recognition that comes with an official visit to the United States. They include Hun Sen, the tyrant who has dominated Cambodia for the past 30 years; Prayuth Chan-ocha, the general who overthrew Thailand’s elected government in 2014 and since has dismantled its democratic institutions; and Najib Razak, the Malaysian prime minister who has carried out a massive crackdown on domestic opponents in the past year while fending off major corruption allegations.

Even Burma, where the opposition recently won a democratic election, will be represented by an autocrat, since the summit was timed ahead of the departure of Thein Sein, a former general installed in power by the armed forces. Only Indonesia and the Philippines will be represented by democratic leaders.

The White House has evidently judged that the strategic benefits of the meeting outweigh the spectacle of Mr. Obama hosting a crowd of strongmen. But the administration could take steps to mitigate the damage to what Mr. Obama has said is one of the priorities of the rebalancing, promoting democracy and human rights.

So far there is not much sign of it. Secretary of State John F. Kerry spoke up about democracy when he visited Cambodia last month and met with an opposition parliamentarian. But Hun Sen will be welcomed in Sunnylands even though the opposition’s leader, Sam Rainsy, remains in exile after being sentenced to prison on trumped-up charges.

For his part, Mr. Obama said nothing about human rights when he met Mr. Najib at the ASEAN summit in Kuala Lumpur in November. Instead, he lauded a “relationship between the United States and Malaysia [that] has strengthened on a whole variety of fronts.” Given that Mr. Najib has been firing government ministers and jailing critics who questioned how $670 million appeared in his personal bank accounts, that was a startling omission.

There should be no such silence in Sunnylands. The Cambodian, Malaysian and Thai leaders, along with those of Burma, Brunei, Laos, Singapore and Vietnam, will want to portray their appearance alongside Mr. Obama to domestic audiences as proof of their legitimacy. The president can send a different message with the words he chooses. He should mention the importance of holding fair elections in Cambodia with Sam Rainsy’s participation; he should talk about Anwar Ibrahim, the Malaysian opposition leader imprisoned a year ago. He should call for a return to democracy in Thailand and the release of political prisoners in Burma. In doing so, he can show that an invigorated U.S. engagement in Asia is based on values and is not just a contest for power with China.