WASHINGTON (REUTERS) - United States (US) First Lady Michelle Obama is expected to steer clear of controversial issues such as human rights when she visits China this week but her trip could help advance a top item on her husband's foreign policy agenda: deepening Washington's ties with Beijing.

The week-long trip marks only the third foreign solo trip for Mrs Obama, who has cultivated a self-described "mom-in-chief" image, putting her energy into raising her daughters Malia, 15, and Sasha, 12, and signature domestic policy issues such as combating childhood obesity.

She has joked that her motto during her husband's White House tenure has been to "do no harm". In keeping with that cautious approach, the White House said Mrs Obama's message on the trip will focus on cultural ties between the two countries and "the power and importance of education" for young people in both countries.

But her trip, which will be front-page news in China and closely parsed by media, will carry important symbolic value.

"There's no better surrogate for a president overseas than their spouse," said Ms Anita McBride, who was chief-of-staff to former First Lady Laura Bush.

Ms McBride said Mrs Obama's visit with Chinese First Lady Peng Liyuan can send a powerful diplomatic message, even if what they discuss has little to do with pressing bilateral issues.

"Those are images that convey a relationship," she said.

Mrs Obama will also visit with students and schools, and take her daughters to see the famous Terracotta Warriors.

Since taking office in 2009, President Barack Obama has put a high priority on bolstering the US relationship with China.

That goal could take on even greater significance given the deep rift has opened up between the US and Russia over the Ukraine crisis.

Former First Ladies Laura Bush and Hillary Clinton used their time in the international spotlight to forcefully elevate tough questions about human rights abroad.

In 1995, Mrs Clinton, wife of former President Bill Clinton, criticised China's human rights record in a speech at a United Nations conference in Beijing.

But it is unlikely that Mrs Obama, a Harvard-educated lawyer, will follow in their path.

"She has chosen a more traditional, non-confrontational role as a first lady," said Ms Laura van Assendelft, a political scientist at Mary Baldwin College. "Other first ladies have pushed those boundaries. Michelle Obama is not pushing any boundaries."

As First Lady, Mrs Obama travelled to Mexico in 2010 and to Africa the following year. A private trip to Spain in 2010 with daughter Sasha backfired when she was criticised for spending taxpayer funds on security for what amounted to a holiday.

Now that her husband is in his second term, and does not have to worry about being re-elected again, Mrs Obama may take more foreign trips to advance policy goals, Ms McBride said.

"You begin thinking about what you want to leave behind,"said Ms McBride, now at American University in Washington.

Mrs Bush travelled to 67 countries to talk about human rights and global health issues during the four years that Ms McBride worked with her, including a notable visit to a refugee camp on the Thai-Burma border to shine a spotlight on conditions there.

THREE GENERATIONS

Mrs Obama will deliver another strong, if unspoken, message by taking her daughters and her mother, Mrs Marian Robinson, with her to China, said Mr Robert Daly, director of the Wilson Center's Kissinger Institute on China and the US.

Mrs Robinson lives with the Obama family in the White House.

"The Chinese are very big on three generations under one roof. That is one of the cornerstones of their culture," Mr Daly said. "That will play very well in the Chinese media."

Pictures of the three generations of four strong women will make a statement about women's equality and opportunity, and shatter a stereotype long held by Chinese about how Americans mistreat their elders, he added.

Mrs Obama's visit comes before her husband visits Asian allies Japan, South Korea, Malaysia and the Philippines in late April, a trip where the maritime dispute with China is expected to loom large.

China and Japan each claim sovereignty over a group of uninhabited islands in the East China Sea, and China is also fighting over territory in the South China Sea with the Philippines, Vietnam, Taiwan, Malaysia and Brunei.

Ahead of the President's trip, the White House will want "sweetness and light" from Mrs Obama's China visit, said Mr Dan Blumenthal, an adviser on China issues in the former George W. Bush administration.

"She can just be who she is, and it's a win. She doesn't have to carry a tough message," said Mr Blumenthal, now director of Asian studies at the American Enterprise Institute think tank.