BANGKOK, Thailand  — Bound for the Beijing Olympics, President Bush is carrying a message of “deep concerns” about the state of human rights in China and urging the communist nation to allow political freedoms for its citizens.

“America stands in firm opposition to China’s detention of political dissidents, human rights advocates and religious activists,” Bush will declare in the marquee speech of his three-nation Asia trip.

“We speak out for a free press, freedom of assembly and labor rights — not to antagonize China’s leaders, but because trusting its people with greater freedom is the only way for China to develop its full potential.”

Bush will deliver the address in a Bangkok, Thailand, convention center Thursday to a crowd of foreign diplomats before flying to China later that day.

The White House released the text of the president’s speech today, nearly 18 hours in advance, as Bush traveled to Thailand from South Korea. Bush arrived in Bangkok today and met with Thai Prime Minister Samak Sundaravej.

Bush’s speech was planned as a summary of what he says is the “stronger engagement” with strategically crucial Asia that has marked his presidency.

But his remarks on China, among his most directly critical ever in public, stand out.

He says he has built a relationship with China’s leaders — through opposing independence for Taiwan, cooperating in negotiations over North Korea’s nuclear program and sharing economic interests, for example — that has allowed him to be “honest and direct” on sensitive internal matters.

“I have spoken clearly, candidly and consistently with China’s leaders about our deep concerns over religious freedom and human rights,” Bush said in the prepared text.

Earlier today, during a news conference in Seoul with South Korean President Lee Myung-bak, Bush said China’s pre-Olympics crackdown on dissent has been “a mistake.”

The communist country considers the Olympics a source of huge national pride and is pulling out all stops to ensure no embarrassments. It has rounded up dissidents, detaining some. Journalists covering the games have objected to restrictions on Internet sites, worried about possible censorship.

Bush objected, saying, “You ought to welcome people being able to express their minds.”

In Thursday’s speech, the president is softening his message somewhat by saying any changes in China would have to come “on its own terms and in keeping with its own history and traditions.”

“Ultimately only China can decide what course it will follow,” he says.

Still, his strong words are likely to anger the leadership in Beijing.

Bush already drew the ire of Chinese officials by meeting ahead of his trip at the White House with prominent Chinese exiles and dissidents.

Bush has made clear that while he is going to Beijing mostly as an Olympics fan, he would talk frankly with Chinese President Hu Jintao during their private meetings. It was also known that he would speak publicly about religious freedom after attending a Beijing church service and that the White House was trying to arrange other meetings while he is in Beijing over four days.

In addition, White House press secretary Dana Perino said the U.S. would protest China’s decision to deny a visa for former Olympic speed skater Joey Cheek, who was planning to travel to Beijing to urge that the Chinese government help make peace in the war-torn Darfur section of Sudan.

“We are taking the matter very seriously,” Perino said Wednesday. “We would hope that they would change their minds.”

Bush’s Bangkok remarks devote only a few sentences to criticism for the “tyranny” in Myanmar, Thailand’s neighbor, which is ruled by a military junta. He called for the release of the country’s democracy icon, Aung San Suu Kyi, as well as other political prisoners.

Though Samak, the Thai prime minister, regards himself as a friend of Myanmar’s generals, Bush heaped praise on his Thai hosts, calling them close allies in the war on terror and noting they’ve sent troops to Iraq and Afghanistan.

Bush noted he’s meeting with exiled activists while in Thailand, and his wife is traveling to the Myanmar border to visit a resettlement camp and clinic. “She’s looking forward to the trip, and I’m looking forward to hearing her report from the trip,” he said, adding, “We want to see freedom and prosperity restored to Burma.”

Bush also congratulated the people of Thailand “for restoring its democracy.”

A bloodless 2006 army coup toppled former Prime Minister Thaksin Shinawatra Thaksin from office. The interim government relinquished power after more than a year in office, allowing a democratic election last December that saw Thaksin’s ally Samak sweep into power. Samak has been accused of trying to change the constitution to hold onto power and to prevent Thaksin from facing corruption-related charges.

Bush kicked off the last Asia tour of his presidency in South Korea.

From there, at Lee’s side, he offered poverty-wracked North Korea hope that it could someday share in its southern neighbor’s economic prosperity and spoke of a future in which it is no longer part of the “axis of evil” he first outlined in 2002.

First, though, he said the reclusive Stalinist regime must meet the step-by-step denuclearization demands contained in a framework agreement reached in six-party talks involving both Koreas, the United States, Japan, China and Russia. The North must also improve its human rights record, Bush said.

“North Korea traps its people in misery and isolation,” the president said.

North Korea expects Bush to remove it from the U.S. list of terror-sponsoring countries as soon as next weekend, as the president said he would when the North destroyed its nuclear reactor cooling tower in June. That offer has always been contingent on North Korea providing a full account of its nuclear activities.

Bush said North Korea — which has a history of unpredictability and has repeatedly used negotiations over its nuclear program to wring aid and concessions from the West — must first do its agreed-upon part and accept international terms for verifying its dismantlement efforts. “I don’t know whether or not they’re going to give up their weapons,” Bush said.