Myanmar's Foreign Minister Wunna Maung Lwin talks with U.S. Secretary of State John Kerry before a gala dinner at Myanmar International Convention Centre in Naypyitaw Saturday. (Soe Zeya Tun/Reuters)

The Obama administration claims the rapid shift away from military dictatorship in Burma as a rare foreign policy success, both for the advance of democratic principles and in the shadowy contest with China for influence and market share.

But the shift is uneven and incomplete, and as Secretary of State John F. Kerry heralds the country’s progress during a two-day visit this weekend, signs of backsliding on human rights and political freedoms are mounting.

Human rights groups and a growing list of congressional critics say the administration is overeager and its enthusiasm misplaced. U.S. leverage to encourage democratic advances has declined since the lifting of major punitive sanctions, although significant economic restrictions remain in place.

Sens. Mark Kirk (R-Ill.) and Marco Rubio (R-Fla.) wrote to Kerry on Thursday to warn against too warm an embrace of the nominally civilian government. The military remains largely in charge behind the scenes, and the senators charged that the ruling party has blocked meaningful constitutional reform.

Without the changes, opposition leader Aung San Suu Kyi cannot run for president next year in elections the United States holds up as evidence of the country’s progress.

A Buddhist monk walks at the shwedagon pagoda in Yangon. Myanmar faces being called to account for stalling reforms when it hosts a top global diplomats at a security forum later this week. (Ye Aung Thu/AFP/Getty Images)

“The ruling party has opposed constitutional changes that would level the playing field heading into the 2015 elections,” the senators wrote. “The military controls access to all significant constitutional change, an arrangement that cannot be acceptable in any society that aspires to democracy.”

As many as 70 political parties could compete in the elections next year, many of them reflecting the ethnic rivalries that have consumed Burma for generations. The main players are Suu Kyi’s opposition National League for Democracy and the ruling military-backed Union Solidarity and Development Party.

Rights groups and some congressional critics worry that a timely, if flawed, election will still be a feather in the leadership’s cap that diminishes the pressure for constitutional changes. In the meantime, progress toward greater political openness has slowed.

In July, four journalists were sentenced to 10 years of hard labor. In May, a draft law was proposed that would outlaw interfaith marriage, a move that rights groups say would open Burma’s already persecuted Muslims to greater discrimination. In both instances, the Obama administration issued fairly mild denunciations.

The muted responses reflected Washington’s deep investment in the new Burmese government, while new U.S.-backed governments in Iraq, Afghanistan, South Sudan and elsewhere falter on the path to democracy. Burma also stands as an important marker of U.S. power in a region nervous about Chinese military and territorial expansion, and a tangible symbol of the Obama administration’s foreign policy turn to Asia.

“We’re here at a pivot point. The country has moved a very great distance from a point of absolute dictatorship and has done a lot of the understandably easier things that one has to do in that process,” a senior State Department official said Saturday as Kerry conducted a round of meetings with Burmese leaders and Southeast Asian diplomats.

“They are now facing some of the deeper challenges — challenges that relate to the heart of what it means to change the government structure of this country,” the official said. “That has produced, predictably, some resistance and some slowdown. This visit was a chance for the secretary to raise some of those core challenges directly and very candidly with the leadership.”

Myanmar democracy leader Aung San Suu Kyi waves to supporters as she leaves from the National League for Democracy party headquarters after she attends the 67th Martyrs' Day in Yangon, Myanmar. (Lynn Bo Bo/EPA)

The official spoke on the condition of anonymity to outline Kerry’s visit.

Kirk and Rubio asked Kerry to make clear “that the status quo in Burma is unacceptable and that meaningful and irreversible progress on these issues is necessary to further advance our bilateral interest in normalizing relations.”

Other congressional critics, including many Democrats, have accused the Burmese leadership of failing to stop ethnic violence and, in some cases, encouraging it. Human Rights Watch and other rights groups say the government has turned a blind eye to land grabs by cronies of the Naypyidaw leadership.

Kirk and Rubio asked Kerry to spend as much time with critics of President Thein Sein as with the leaders, which State Department officials said was impossible because of time constraints. Kerry’s trip was shortened because of an emergency trip to Afghanistan on Thursday and Friday to ride herd on that country’s feuding political rivals.

Kerry was to see Suu Kyi in the commercial capital, Rangoon, on Sunday but will not meet with other political or human rights activists. Most of his visit will be in this newly constructed inland capital, where many of the gleaming buildings were built by the Chinese.

Suu Kyi was released from years of house arrest and won election in 2012 as an opposition member of parliament. She was initially a cautious partner to the military-backed leadership but is now openly critical.

The country of about 60 million people remains one of the poorest in the world. Although the military leadership’s decision to distance itself from China three years ago opened the door to change, Chinese investment far outpaces that of the United States — about $14 billion compared with about $243 million.

The administration contends that it has eased sanctions only on a quid pro quo basis: Burma makes specific progress and gets a specific reward. Rights groups say the benefits to Burma are outpacing reforms.

Burma, also known as Myanmar, seeks the lifting of remaining U.S. sanctions and the opening of military-to-military ties. The latter may be the more powerful leverage for continued change. Despite new freedom to do business in Burma, many potential investors have stayed on the sidelines, citing the uncertain political state, a lack of reliable electricity and a dearth of qualified workers.

Still, as Kerry’s visit highlights, the turnaround in Burma is significant.

Inside four years, Burma has gone from international pariah state to host of a major regional forum that is expected to draw President Obama for his second visit as president later this year. The juntas stepped aside, construction is booming, rents are rising and American businesses are nosing around for deals as Burma courts international investors.

“It’s impossible not to be impressed by the steps that the government has achieved, the road and the journey that they are on to reform and to transition,” Kerry said after meetings with the Burmese president and parliamentary leader. “As Myanmar tackles the challenges ahead, I want the people of Myanmar to know that they have the support and friendship of the United States.”

Kerry gave no public accounting of those challenges or the U.S. view of them, but aides said he did so in private.

The secretary of state is attending a run-up to that showpiece summit of the Association of Southeast Asian Nations, or ASEAN.

The United States pivoted from trying to freeze out Burma from a prominent role in ASEAN to championing the nation as chairman and host of the gathering this year. The status conferred as the forum host is symbolic but potent, not least as an inducement to business.

“The fact that they have embarked on such a significant political reform sufficient to become the chair, and that they are thus far doing a good job as chairman, is pretty important and pretty impressive,” said a second senior State Department official, also speaking on the condition of anonymity to outline Kerry’s agenda.