"There's no one reason we lost," Priebus said of November's election, in which Democrats held the White House, kept control of the Senate, and gained in the House. "Our message was weak, our ground game was insufficient, we weren't inclusive, we were behind in both data and digital, and our primary and debate process needed improvement."
Priebus added: "When Republicans lost in November, it was a wake-up call. We know that we have problems. We've identified them, and we're implementing the solutions to fix them."
House Majority Leader Eric Cantor (R., Va.) declared the plan a "fantastic job by all involved," while former House Speaker Newt Gingrich hailed it as "historic" and the "first big step toward [a] GOP majority."
But even many Republicans who praised the proposal said it was only a partial response to the party's problems, which include policy positions that alienate growing minority groups.
Strategists said the party still needs to recast conservatism to appeal to Latino and Asian voters as well as college-educated women.
"We ran out of white voters" in the 2012 election, said Alex Castellanos, a longtime GOP strategist. Republicans still need to establish a policy agenda that goes beyond being "the party of 'no' and an alternative to big, old, slow, top-down industrial-age government," he said.
Championing immigration reform is a productive start, said Mike Murphy, another longtime strategist. But he said Republicans should also adopt a softer stance on other social issues, such as same-sex marriage.
"The most important message from the campaign was that the electorate is changing and we have to be in front of that, not behind it," Murphy said. "Modernizing the mechanics is a great way to communicate to the new electorate, but the most important thing is how do we appeal to them with the policy agenda of a modernized conservatism."
The RNC's "Growth and Opportunity Project" report is the product of a listening tour by Priebus and several leading GOP strategists. "Focus groups described our party as 'narrow-minded,' 'out of touch' and 'stuffy old men,' " Priebus said. "The perception that we're the party of the rich continues to grow."
Some conservative activists quickly found fault with the plan - specifically the RNC's calls to champion immigration reform and shorten the presidential nominating process.
"Americans and those in the tea party movement don't need an 'autopsy' report from RNC to know they failed to promote our principles, and lost because of it," said Jenny Beth Martin, head of the Tea Party Patriots.
Marjorie Dannenfelser, president of the Susan B. Anthony List, said the RNC report draws the wrong lessons from 2012 and said that Republicans should focus more on abortion and other divisive social issues.
"Social issues are keys to reaching certain minorities the GOP yearns to attract, as well as to motivate millions of voters who first gravitated to the party as Reagan Democrats," she said in a statement.
The RNC wants to compress the primary calendar, stage fewer candidate debates, and hold more primaries - which usually attract more mainstream voters - rather than caucuses, which tend to draw devoted partisans.
The proposals amount to an attempted course correction from 2012, when candidates with little funding or mainstream support used their debate performances and strong showings in caucuses to mount extended challenges to Mitt Romney, the eventual GOP nominee. Many party strategists think the process weakened Romney in his general-election fight against Obama.
But to many grassroots conservatives, the rule changes would give establishment candidates further advantages and limit the opportunities for insurgent candidates such as Rep. Ron Paul, who struggled to win mainstream support but performed well in caucuses last year.
The RNC's road map comes on the heels of last weekend's Conservative Political Action Conference, the biggest annual gathering of conservative activists, which brought new attention to the divergent ideas now coursing through the Republican Party.