WASHINGTON — President Obama on Monday requested more than $1.8 billion in emergency funding to fight an outbreak of the Zika virus, which has spread to 26 countries and territories in Central and South America, though not yet to the United States.

The money would go toward expanding programs that control mosquitoes, which transmit the virus, as well as research into vaccines and new public education programs, particularly for pregnant women, the president said in an interview on “CBS This Morning.”

Brazil, which has been among the countries hardest hit by the virus, has reported a significant increase in the birth of babies with abnormally small heads, a condition that may be linked to the virus.

Mr. Obama’s request to Congress came as the White House was trying to strike a balance between being responsive to the outbreak and not provoking alarm. Two years ago, the administration initially played down the risk that the Ebola virus would spread to the United States, only to reverse course after the diagnosis of several cases here. Mr. Obama, angered by the slow response, appointed a special coordinator to handle the outbreak.