SACRAMENTO — Governor Schwarzenegger yesterday rejected the budget passed hours earlier by the Legislature, pledging to veto it for failing to meet his reform demands and solve California’s persistent fiscal problems.

If Schwarzenegger follows through on his threat, it would mark the first time in modern history that a California governor would veto a state spending plan. It set in motion a historic showdown with the Democratically controlled Legislature, which has said it is prepared to override the pending veto.

Mr. Schwarzenegger’s announcement, with a veto coming as soon as today, came after a record-long stalemate that forced the state to delay billions of dollars in payments to schools, medical clinics, daycare centers, and state vendors. Lawmakers finally cobbled together a patchwork spending plan on the 78th day after the start of the fiscal year, passing a $143 billion budget shortly after 2 a.m. yesterday.

He called the budget irresponsible and said the reforms it contained were phony.

“I say enough is enough,” Schwarzenegger said. “California has been put through this roller coaster ride too many times.”