WASHINGTON — In a broad test of his executive powers, President Barack Obama declared Wednesday he will sidestep Congress and order his own federal action on immigration — in measures that could spare from deportation as many as 5 million people illegally in the U.S. and set up one of the most pitched partisan confrontations of his presidency.

Obama declared that Washington has allowed America’s immigration problem “to fester for too long.”

The president will use an 8 p.m. EST address today to announce his measures and will sign the executive actions during a rally in Las Vegas on Friday. In doing so, Obama will be taking an aggressive stand that he had once insisted was beyond his presidential power.

As many as 5 million people in the country illegally are likely to be protected from deportation and made eligible for work permits under the plan. They would not have a path to citizenship, however, and the actions could be reversed by a new president in two years. Officials said the eligible immigrants would not be entitled to federal benefits — including health care tax credits — under Obama’s plan.

The 5 million estimate includes extending deportation protections to parents and spouses of U.S. citizens and permanent residents who have been in the country for five years. The president also is likely to expand his 2-year-old program that protects young immigrants from deportation. The administration had considered extending the executive action to parents of young immigrants covered under the 2012 Obama directive, but immigration advocates said they did not expect the parents to be included in the final plan.

“What I’m going to be laying out is the things that I can do with my lawful authority as president to make the system better, even as I continue to work with Congress and encourage them to get a bipartisan, comprehensive bill that can solve the entire problem,” Obama said in a video on Facebook.

Laying the groundwork for his actions, Obama invited 18 Democratic members of the House and Senate — but no Republicans — to dinner at the White House on Wednesday. Among the networks airing his Thursday speech will be Univision, which will interrupt the Latin Grammys to carry his remarks, assuring him a huge Spanish-speaking audience. The major broadcast networks — ABC, CBS and NBC — were not planning to air the speech, but cable news networks were.

Obama is to speak at Las Vegas’ Del Sol High School on Friday, a school with a large population of non-English speaking students where Obama unveiled his blueprint for comprehensive immigration legislation in 2013.

Republicans vehemently oppose the president’s likely actions but are deeply divided and have spent much of the week intensely debating how to respond. Some conservative members have threatened to pursue a government shutdown and one — two-term Republican Rep. Mo Brooks of Alabama — raised the specter of impeachment on Wednesday.

House Speaker John Boehner’s spokesman criticized Obama’s planned announcement, noting that the president himself had said in the past that he was not “emperor” and was limited in his ability to act.

“If ‘Emperor Obama’ ignores the American people and announces an amnesty plan that he himself has said over and over again exceeds his constitutional authority, he will cement his legacy of lawlessness and ruin the chances for congressional action on this issue — and many others,” the spokesman, Michael Steel, said.

A wide-ranging immigration bill passed the Senate last year, but stalled in the Republican-led House. Senate Democratic leaders on Wednesday took turns declaring their support for Obama’s unilateral action, blaming Republican inaction for forcing Obama to act.

“There’s one more chance: Just put the bill on the floor, Speaker Boehner,” said Sen. Chuck Schumer, D-N.Y., a lead author of the bill that passed the Senate. “Pass the bill and we will not even have to debate executive action.”