President Barack Obama’s senior adviser and his top lawyer were blunt with liberal activists on a strategy call as they jumped into what political professionals in Washington expect to be one of the hardest-fought Supreme Court battles in a generation.

In what one participant described as part pep rally and part planning session, Valerie Jarrett, a senior adviser to Obama, and Neil Eggleston, the White House chief counsel, urged dozens of the president’s allies who were on the phone not to hold back in their condemnation of Republicans for refusing to hold hearings to replace Justice Antonin Scalia, who died last week.

The White House hardly needed to prod the interest groups during the Tuesday call. The outcome of this battle could determine the fate of a vast array of contentious issues for decades to come. So in record time, the liberal and conservative Washington lobbying and advocacy machines are roaring to life. Advocacy groups are already vowing to spend millions of dollars.

“It’s going to be the entire progressive movement up against the entire conservative movement,” said Frank Sharry, an immigration activist whose organization was represented in Tuesday’s White House call. “I do think it’s going to be a battle of a different order.”

On Wednesday, White House officials responded to Republican accusations of hypocrisy by Obama, who voted to filibuster President George W. Bush’s nomination of Samuel A. Alito Jr. to the court. Obama — who is now demanding a quick hearing and vote for his next nominee — regrets that vote, said Josh Earnest, the White House press secretary. Earnest said the president did not believe Democrats should have been “looking for an opportunity to throw sand in the gears.”

Like their liberal counterparts, the leaders of conservative groups have jumped to reorder their priorities. Moments after Scalia’s death became public, the American Center for Law and Justice organized a team of five lawyers to scour the backgrounds of potential nominees, and another team to research the Senate’s procedural rules.

“The stakes are as high as anything we have dealt with in Washington in a decade,” said Jay Sekulow, the chief counsel for the law center. “This is not even the beginning of what this fight will be. It’s full-media, full-legal research, full-government affairs, full-throttle on this.”