WASHINGTON — On the day after President Barack Obama’s historic announcement of a plan to protect millions of illegal immigrants from deportation, hundreds of Latino activists and families gathered in front of the White House Friday afternoon to express their gratitude – and vow to press Congress to finish the job.

“The decision of the president is going to change the lives of 5 million people forever,” said Gustavo Torres said beore the rally. He is executive director of CASA de Maryland and Virginia, the major regional advocacy group for illegal immigrants.

“Today is a day for all of us to celebrate and thank him for delivering on his promise,” he said. “We are all very touched and moved by what he has done.”

At the same time, Torres said Friday will be the “last day of celebration,” because the immigrant community needs to turn its attentions immediately to Congress and the unfinished business of comprehensive immigration reform.

“We need to get ready to continue the fight,” said Torres, whose organization is one of five groups that sponsored the rally in Lafayette Square. “We have made history, but we cannot wait, because millions of people have still not gotten the help they need. We need to start pushing the Republican Party really hard to pass a bill.”

Some immigrants at the rally, which was attended by about 200 to 300 people, expressed mixed emotions about Obama’s announcement. They said they were grateful for his efforts but disappointed that the president had stopped short of legalizing several million other people, including many adults with no children and others whose children were legalized under his 2012 order.

A few feet away from the rally, a protester in military fatigues shouted through a bullhorn, “You are all illegal” and “Obama is the number one coyote,” using a word for guides who smuggle migrants into the United States. The man refused to identify himself.

The president’s action is expected to benefit about 4 million of the nation’s estimated 11 million illegal immigrants. CASA officials have predicted that could include up to 100,000 people in the Washington region, mostly from El Salvador, Honduras and Guatemala, who are parents of U.S.-born children or arrived in the country as children.