JEFFERSON CITY, Mo. (AP) -- A key Republican House member is questioning the legality of Gov. Matt Blunt's plan to expand government-subsidized health care to more low-income parents.

Blunt's administration filed proposed rules for the new Insure Missouri program on Wednesday and plans start enrolling participants next month. But Rep. Rob Schaaf is leading a special House committee that has been casting a particularly critical eye on Blunt's plan.

"I don't believe they have the legal authority to start the program," Schaaf, a Republican physician from St. Joseph, asserted Thursday.

Blunt insists he is on firm legal ground, granted by lawmakers themselves.

The state budget "allows us to create this program, expand access to care," Blunt told reporters Friday in Ashland. "We're operating, I think, within the confines of the bill."

But the dispute underscores the resistance the Republican governor faces from some within his own party as he tries to roll out one of his top priorities for 2008. Republican House leaders are trying to arrange a time next week for Blunt to speak privately to the Republican caucus about his plan.

Insure Missouri initially could cover an estimated 55,000 working parents living in poverty, defined as about $20,650 annually for a family of four. Over the following four years, Blunt wants to expand it to cover nearly 190,000 people at a cost of $952 million in state, federal and private dollars.

The program would restore coverage to some, but not all, of the people dropped from Missouri's Medicaid rolls by Blunt's 2005 budget cuts. Although the program would be administered by the state's Medicaid division, recently renamed as Mo HealthNet, the enrollees would be covered by private insurance companies contracting with the state.

Blunt took many lawmakers by surprise when he announced Insure Missouri last September, because the Mo HealthNet law they passed had authorized a pilot project in which the state would pay a portion of the private insurance premiums of some low-income Missourians.

But Blunt's administration decided that was unworkable and instead relied on a provision in a separate budget bill to launch a bigger and broader statewide program paying almost the full cost of health insurance for some of the estimated 772,000 people now lacking it.

That budget bill appropriated $5 million in state general revenues, $8.2 million in federal money and an unspecified amount in hospital taxes for either the type of program envisioned in the Mo HealthNet bill "or a program that will promote private health insurance coverage for certain low-income employees."

During a committee meeting Thursday, Schaaf questioned whether that budget provision allowed a program providing -- as opposed to merely promoting -- health insurance. He also questioned whether the Insure Missouri program truly was private health insurance, since the government is paying virtually the full cost of it.

Brian Kinkade, the deputy director of Blunt's Department of Social Services, insisted it is private insurance because the state will be contracting with insurance companies instead of paying medical providers directly.

"The department has undertaken Insure Missouri with the full belief it comports with the provision of this section," Kinkade told the committee.

But Schaaf kept raising concerns. He noted the budget bill allows the department to "pursue coverage for adults" with incomes below the federal poverty level. But Schaaf suggested Blunt's administration may be illegally narrowing the focus by limiting the initial program only to parents who are at least age 19.

Kinkade said the department simply needed a way to phase in the program.

Upset as he may be, neither Schaaf nor his Special Committee on Healthcare Transformation has the power to block the Insure Missouri program from taking effect. Schaaf suggested that a lawsuit could try to prevent it from starting on the same grounds he cited, but said he did not have the money to personally pursue such a case.