ALBANY – Governor Pataki vetoed a bill yesterday that would allow legislators to rewrite the budget when agreement with the executive is not reached by a new May 1 deadline.

The bill, first proposed and vetoed last year, would implement a proposed constitutional amendment that legislators plan to put before the voters in a statewide referendum in November. The referendum will go forward despite the governor’s opposition because legislators from both chambers have approved the changes in two consecutive sessions.

The amendment would reduce the powers of the governor’s office by putting legislators in charge of writing budget bills once the deadline is not met. Legislators could also avoid criticism for late budgets because of a provision that provides for a contingency budget to take effect while they work on a budget of their own.

The proposed power shift has caused some to wonder whether the state attorney general, Eliot Spitzer, would come out in opposition to the proposed amendment. Mr. Spitzer, the presumptive Democratic candidate for governor next year, has been reluctant to wade into policy debates. The coming debate over the amendment is viewed as an early sign of his political will.

Mr. Spitzer’s spokesman, Marc Violette, was careful to express opposition to the amendment while avoiding discussion of its potential impact on the powers of the governor. Mr. Violette said budget reform should be brought about through statutory and rule changes rather than constitutional amendments.

Mr. Pataki, asked yesterday whether he would mount a campaign against the amendment, said simply he has “reservations” about it. That tepid level of opposition could signal Mr. Pataki’s lack of interest in serving another term.

Opponents of the change have argued that an on-time budget this year is evidence that budget reform is not necessary. But a spokesman for the majority leader of the Senate, Joseph Bruno, a Republican of Rensselaer, said the change would make on-time budgets the rule rather than the exception.

“This will put an end to late budgets, and we believe the voters will support it in the fall,” the spokesman, Mark Hansen, said.

In vetoing the bill, Mr. Pataki was siding with a change to the state budget that was brought about in 1927 by Alfred Smith. Governor Smith pushed for increased executive control over the budget, saying legislators are accountable only to voters in their districts while the governor is accountable to all residents.