ALBANY – For state lawmakers, the fear isn’t that Governor Pataki will veto portions of their budget – it’s what he’ll do when they override him.

While the governor is concealing his endgame strategy, lawmakers in both houses are taking seriously the possibility that Mr. Pataki could simply ignore their most precious appropriations and get away with it.

Some in the Legislature are calling it the governor’s “nuclear option.” One lawmaker, without a note of irony, is calling it “democracy’s worst nightmare.”

The governor is accusing the Legislature of overstepping its constitutional powers by altering language in the appropriations bills of his executive budget.

Specifically, he’s casting doubt on the constitutionality of a property tax rebate check program in the legislative budget. The governor wants the checks reserved for residents living in school districts that adopt a spending cap, but lawmakers tossed out the restriction in their budget and approved a rebate check program that would benefit homeowners statewide. Senate Republicans are counting on those checks being mailed out to voters just before November’s elections.

Taking aim at the Assembly’s budget priorities, Mr. Pataki is questioning the Legislature’s restoration of hundreds of millions of dollars in Medicaid spending. The governor is contending that the spending add-ons required unconstitutional language changes, though his office wouldn’t provide specifics.

The threat from Mr. Pataki is changing the dynamic of budget negotiations, coming as a surprise to legislators who assumed that they possessed all the leverage. They felt confident that they could override any budget vetoes, but say they aren’t sure about how to deal with the governor’s legal tactics. Tomorrow is the deadline for the governor to veto the state budget.

“We’ve never faced it before,” a Republican senator of Long Island, Michael Balboni, said.

For Mr. Pataki, a lame-duck governor with dwindling political power, the unusual tactic is his best chance to bend the will of the Legislature, particularly on the issues of education tax credits, charter schools, and Medicaid spending.

The Democratic speaker of the Assembly, Sheldon Silver, said yesterday he wasn’t cowed by the governor’s threat and said lawmakers were passing a supplemental budget bill that would address the governor’s legal concerns.

“When I went to law school, the one thing you learned: If you’re wrong on the law, if you’re wrong on the facts, dazzle them with your baloney. I think that’s what the governor is trying to do,” Mr. Silver told The New York Sun.

“There’s no leadership,” he said. “You have a governor of technicalities.”

He said he has no intention of softening his opposition to the governor’s education tax credit plan, which gives tax relief to parents who spend money on private school tuition. Lawmakers approved a more general tax credit that isn’t linked to educational expenses.

Assemblyman Richard Brodsky, a Democrat who represents a district in Westchester, had a more dramatic reaction: “This is democracy’s worst nightmare. This is the king telling the parliament they can’t change the law. This is absolutely devastating to our ability to check executive power.”

Such a move on the governor’s part would be difficult for legislators to counter. If they mount a legal challenge, they could risk delaying spending that lawmakers are relying on to curry favor with voters. And there’s no guarantee that the surplus money they want to spend this fiscal year will be available next year.

Mr. Balboni said if voters’ property tax rebates are held up because of a legal dispute, they would hold Mr. Pataki responsible, not lawmakers. “Here we’re cutting taxes, and he’s saying, ‘I’m not going to enforce them,'” he said. “We’re on the side of angels.”