Gov. Robert F. McDonnell (Bob Brown/ Richmond Times-Dispatch via AP)

“A great expansion of Medicaid, without significant reform of the so-called ‘federal-state partnership,’ is not responsible,’’ McDonnell wrote.

Six other Republican governors have announced that they would not participate.

In a seven-page letter to members of the General Assembly, McDonnell said he was weighing ramifications following the Supreme Court’s health-care decision. But he reiterated that he would not call a special legislative session to deal with the issues.

States are required to set up exchanges for residents to purchase health insurance, but the General Assembly did not do so this year in hopes that the Supreme Court would find the federal law unconstitutional.

Virginia originally had until last month to apply for a grant to help pay to set up the health exchange, but the federal government has added additional deadlines for grants.

“With multiple unanswered questions and great uncertainty, it is not prudent to spend a great deal of time and taxpayers’ money on building a system that we may never need to implement or that may be materially different once the rules are finally established,’’ McDonnell said.

He said that he hopes a new Congress and president will repeal the law that he considers a massive unfunded mandate.

McDonnell, chairman of the Republican Governors Association, also sent a letter on behalf of Republican governors to President Obama seeking clarification on critical outstanding questions related to the federal health-care law in the wake of the Supreme Court’s decision.