WASHINGTON (Reuters) - U.S. lawmakers and 30 human rights groups on Thursday urged President Barack Obama to use a weekend summit with Chinese President Xi Jinping to press for the freedom of 16 prominent political and religious prisoners.

The "China 16" include imprisoned Nobel Peace laureate Liu Xiaobo, rights lawyer Gao Zhisheng and political prisoners from the Tibetan and Uighur ethnic minorities, Christians and followers of the banned Falun Gong spiritual movement.

Obama hosts Xi in California on Friday and Saturday for what both countries have billed as an informal summit focusing more on developing personal chemistry than on resolving specific disputes between the world's two biggest economies.

The 16 prisoners were "only the tip of the iceberg among hundreds of thousands of cases," blind legal activist Chen Guangcheng told a news conference in Washington, speaking by video from New York.

Chen made international headlines last year when he escaped house arrest and took refuge at the U.S. Embassy in Beijing before flying to exile in New York to study law.

The 30 rights groups include Amnesty International, Jubilee Campaign and the International Campaign for Tibet and are backed by Democratic and Republican lawmakers. They called on Obama to restore human rights as a central issue in U.S.-China relations - as it had been in the first two decades after diplomatic ties were established in 1979.

"(We) call upon you to advocate for the rights of prisoners of conscience, as your predecessors have done," Republican Representatives Frank Wolf of Virginia and Chris Smith of New Jersey and Democratic Representatives James McGovern of Massachusetts and Karen Bass of California said in a letter to Obama.

A senior Obama administration official told reporters on Tuesday that, "As always, the president will forthrightly - and I think persuasively - raise American human rights concerns."

U.S. presidents routinely used to champion individual rights cases and during Bill Clinton's 1993-2001 tenure in the White House, China released well-known political prisoners on humanitarian grounds before bilateral summits.

But such releases have become rare since the United States gave Beijing permanent trading privileges in 2001, when China joined the World Trade Organization, ending an annual vote by the U.S. Congress based on a review of China's record.

"We all know how dangerous it is to get our hopes up, because we have had our hopes dashed on more than one occasion," Ti-Anna Wang told a news conference in Washington, where she has been lobbying on behalf her jailed father and other prisoners.

The 24-year-old Wang's father, Wang Bingzhang, is a physician serving life in prison for his role in overseas Chinese democracy movements. Wang and several other daughters of jailed dissidents fought back tears as they described growing up in exile in the United states, far from their jailed fathers.

(Reporting by Paul Eckert; Editing by Cynthia Osterman)