PRESIDENT REAGAN broke longstanding tradition yesterday by signing a major piece of legislation -- the job-training bill replacing the expiring CETA program -- without any of its congressional sponsors present for the ceremony. It's a fitting conclusion for a long legislative struggle in which Congress bent over backward to speed passage of the legislation while administration officials did their apparent best to impede it.

The president dismissed as "campaign talk" congressional criticism that he had not supported the bill until record unemployment pushed him to last- minute agreement. But the president certainly failed to convey his early enthusiasm to his appointees in the Labor Department. They argued and threatened veto over every jot and tittle for months. Finally, as the recess drew near, Republican congressional sponsors tired of the haggling and took their bipartisan compromise straight to the White House for approval.

The White House is right, however, that what matters now is not how the bill came to passage but what the final measure looks like. It's a pretty good compromise. It continues programs for youth summer jobs, welfare recipients and older workers that the administration had sought to end, and keeps the successful Job Corps running at close to current levels. It sets up a new, although small, program for workers whose jobs have been lost through industrial change. And it increases private-sector involvement and tightens standards in the other adult and youth training programs that will now be folded into grants to states and localities.

The bill doesn't create any new jobs -- and it doesn't ensure any particular level of funding. The conferees estimate the full cost of the programs at $3.7 billion--about the level of funding provided in the continuing resolution. That's $1.3 billion more than the administration sought in its 1983 budget. Even if the higher level is continued next year, the government will be spending far less than the $6.8 billion it spent on comparable programs in 1981.

In signing the bill, President Reagan remarked that the new program is "not a boondoggle." Perhaps the president meant to contrast the new program to its predecessors (from which it actually differs in degree rather than in kind). Or perhaps he meant to reassure the public that his Labor Department intends to do a much better job of administering the program than it did in securing its enactment.