Counties could be forced to raise property taxes by hundreds of millions of dollars if Democrats follow through on their plans to not allow the Senate to reconvene any time soon, county leaders said today.

That’s because bills needed to extend sales-tax laws in 47 counties beyond this November have yet to be approved by the Senate.

“This is going to cause a massive increase in property taxes – doubling of county taxes in some instances,’’ said Stephen Acquario, executive director of the state Association of Counties. “This could cause complete chaos.’‘

The future of the next Senate session is uncertain because control of the chamber apparently changed hands yesterday, with two Democrats defecting from their party to give the majority back to Republicans. The contentious battle for control could end up in court, possibly paralyzing the body for weeks or even months.

State law requires that the Legislature every other year to renew the authority of counties to levy sales taxes above 3 percent. Counties typically have a 4 percent rate – matching the 4 percent that the state charges, although some are slightly higher and a few are lower. The authority for most counties runs out in November.

Acquario said that even if the higher levies are approved later in the year, it will be hard to craft budgets for next year, on which work generally starts in August.

“The Legislature needs to approve these bills now,’’ he said.

The Assembly is considering a bill sponsored by Assemblywoman Sandra Galef, D-Ossining, Westchester County, that would remove the need for renewal by the Legislature, but there is not as yet any matching proposal in the Senate.

Senate Republicans say they intend to start acting on bills tomorrow, but Democrats have said they won’t reconvene until the leadership issue is settled.

“We believe we’re on solid legal ground’’ in reconvening tomorrow, said Senate GOP spokesman Scott Reif.

But Democratic spokesman Travis Proulx said that “only the majority leader can call a session, and the majority leader is still Malcolm Smith.’’