(Repeats to add UPDATE 1 to headline.)

(Updates with details of outbreak)

WASHINGTON, April 26 (Reuters) - Twenty cases of swine flu have been confirmed in the United States as the White House stepped up efforts to monitor the outbreak, U.S. officials said on Sunday.

Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention, said at a White House briefing that all of the U.S. cases have been mild. U.S. officials said President Barack Obama is being briefed regularly on the potential spread of the new strain of flu, which has taken as many as 81 lives in Mexico.

"At this point, a top priority is to ensure that communication is robust and that medical surveillance efforts are fully activated," John Brennan, assistant to the president for Homeland Security, said at a White House news conference.

He said beefed up monitoring would enable rapid identification and notification of any new cases that might occur in the United States and Mexico.

Besser said the CDC has confirmed one case of swine flu in Ohio, two in Kansas and eight in New York. There were already seven confirmed cases in California and two in Texas. Officials emphasized that the U.S. cases are not as severe as the cases that have been identified in Mexico.

Nevertheless, the officials recommended planning for potential U.S. school closures and Homeland Security Secretary Janet Napolitano said the United States would release some of its stockpiles of anti-flu drugs Tamiflu and Relenza. She also said the United States would declare a public health emergency to start the flow of aid to states and communities that might be affected by the outbreak.

(Writing by Donna Smith, editing by Patricia Zengerle)

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