PHOENIX — The fate of a law to expand Medicaid in Arizona is now expected to be resolved by the courts, not the ballot box.

Backers of a referendum drive to put the question on the 2014 ballot acknowledged late Wednesday that they had collected only 81,349 signatures on petitions to force a public vote by Wednesday’s 5 p.m. deadline. They needed at least 86,405.

That means the measure, pushed through the Legislature by Gov. Jan Brewer, became law as scheduled overnight.

But foes of the proposal to add 300,000 or more to the rolls of the Arizona Health Care Cost Containment System contend the law is illegal and are expected to sue to void the measure before the actual expansion starts Jan. 1.

If that fails, they have an ultimate backup plan for 2014: try to oust the Republican legislators who voted with the Democrats for expansion. Tucsonan Christine Bauserman, one of the coordinators of the failed effort, said efforts already are underway to find GOP challengers whom her group, the United Republican Alliance of Principled Conservatives, finds acceptable.

Bauserman pointed out it is the official position of the national Republican Party to repeal the Affordable Care Act, meaning party members who voted to have Arizona participate in it, including the governor, are not good Republicans.

Former state Sen. Frank Antenori, R-Tucson, said the referendum drive he chaired should not be considered a failure because it provides his group with the names of 80,000 individuals who oppose the law and are willing to work to oust those who approved it.

Brewer’s response has been to follow through, beginning next week, on a promise she made to Republicans who backed her to help them raise money for their re-election campaigns.

The law takes advantage of a provision in the federal Affordable Care Act to provide generous reimbursement to states that expand their Medicaid programs to cover anyone with income equivalent to 138 percent of the federal poverty level. Arizona law now covers most individuals only up to the poverty level, about $19,530 a year for a family of three.

But to get that $1.6 billion a year in federal money, it will cost the state an estimated $240 million. That’s because Arizona also needs to reverse its decision of several years ago to cut coverage for childless adults, even those below the federal poverty level. To raise that $240 million, the legislation empowers AHCCCS Director Tom Betlach to assess a fee on hospitals.

The Arizona Constitution requires a two-thirds vote of both the House and the Senate for an increase in taxes or revenues to the state. The legislation did not get that margin.

Brewer, however, contends the levy is an “assessment,” not subject to that requirement.

“There are countless examples where agencies have been given such fee authority,” said gubernatorial spokesman Andrew Wilder, asserting the Legislature has done it more than 80 times in the last five years.

This, however, differs both in scope — it is far larger than anything ever approved before — and in that AHCCCS does not regulate hospitals and the levy is not to cover the costs of the agency in overseeing the facilities.

There also is the question of whether it is legal to give Betlach the authority to levy the fee.

“We are confident in our legal position,” Wilder said.

Brewer, in a prepared statement, called the failure of the referendum “validation that Arizonans see Medicaid restoration as the right thing for Arizona’s future.”

Brewer has pushed the term “restoration” rather than “expansion” because a majority of the 300,000 who will get care beginning Jan. 1 are those who she said should have been receiving it all along.

A 2004 voter-approved measure required the state to provide coverage for everyone below the federal poverty level. And the Arizona Constitution bars lawmakers from tinkering with voter-approved proposals.

But courts refused to reverse the decision by Brewer and lawmakers to stop enrolling childless adults.

Judges pointed out that the language of the 2004 initiative requires the state to use only the proceeds from a tobacco tax, the state’s share of a nationwide settlement with tobacco companies and other “available funds.” They said the question of whether there was cash “available” is political and beyond their right to second-guess the executive and legislative branches.