In an elaborate White House ceremony that rang with both hope and hype, President Carter signed into law yesterday the Civil Service Reform Act, which he said "changes the rules" of the federal bureaucracy in a monumental way for the first time in nearly a century.

Carter said the bill will bring to government the kind of incentive-and-reward system upon which the country was founded and give the taxpayers a better deal from their public servants.

The bill "allows federal employes to be fired for the right reasons - if they cannot or will not perform - and prevent firing them for the wrong reasons - for whistle-blowing or for personal whim . . .," he said.

Carter praised members of Congress as well as his Civil Service Commission chairman. Alan K. Campbell, for their work on the legislation. He called on government workers at every level to help him "get busy and make it work."

Considered a major victory for Carter, the bill's passage enables him to take what he called a "long step" toward redeeming a campaign pledge that he would shake up the bureaucracy on behalf of an electorate outraged over government waste, corruption and seeming insensitivity.

The thick and complex bill reached the president's desk just 16 months after its inception and only seven months after he sent it to Congress. But at first, as Carter noted yesterday, it was an effort which "many people predicted would end in failure."

Carter's is the first successful effort of some 20 attempts to revamp the civil service system since 1937.

Yesterday morning in the state dining room, just a few paces from where the rubbernecking throngs choked the White House corridors, spokesmen for a spectrum of groups from big business to big labor gathered to slap each others' backs, and the president's, for making it all possible.

Rep. Morris K. Udall (D-Ariz.), who managed the bill in the House, tossed a sobering reminder at the crowd. He aid, "I was in this room eight years ago with another president, for a great reform called postal reform - you remember that? . . . "That best reforms aren't going to work unless you make them work."

Kenneth Blaylock, president of the largest federal employes union, the AFL-CIO backed American Federation of Government Employees, drew personal praise from the president for his limited support for the bill "at great potential political cost to himself."

Among the key elements of the legislation are a system tying pay and promotions to performance, rather than length of service; an elite corps for senior executives enabling them to trade job security for a chance at bonuses for superior performance; streamlined procedures for hiring and firing employes and new protections against reprisals for employess who blow the whistle on waste or wrongdoing by their bosses.