HELENA — Rep. Denny Rehberg, the only Republican in Montana’s congressional delegation, is not endorsing the controversial federal spending plan unveiled this week by GOP House Budget Committee Chairman Paul Ryan.

Instead, Rehberg, who’s in a tight U.S. Senate race against Democratic incumbent Jon Tester, said Tuesday that he’s going to “study Congressman Ryan’s new proposal very carefully,” and talk to Montanans before deciding what he’ll support.

Montana’s two Democratic U.S. senators, however, had no such doubts about where they stand, blasting the Ryan plan this week as something that would dismantle the Medicare program and grant big tax cuts to the wealthy and corporations.

“Seniors would face serious cuts to critical health-care services, benefits would decrease and costs would soar,” Sen. Max Baucus said in a prepared statement. “The plan does nothing to lower costs; it only shifts costs onto the backs of seniors. ...

“Any way you spin it, ending Medicare is wrong and I won’t let it happen on my watch.”

Tester’s Senate campaign also released a statement Tuesday, saying he won’t support the plan.

“Cutting taxes for wealthy corporations while at the same time proposing hundreds of billions in cuts to Medicare is as irresponsible as it gets for Montana,” said Tester’s campaign manager, Preston Elliott.

Ryan, a Republican from Wisconsin, unveiled his budget proposal Tuesday, saying it provides a path to cut federal deficits and boost the economy — and offers a stark contrast to Democrats’ proposals.

The plan wipes out all but two federal income tax brackets, cutting the top rate from 35 percent for the wealthiest taxpayers to 25 percent. The other tax rate would be 10 percent. It also cuts the top federal corporate income tax rate from 35 percent to 25 percent.

On the spending side, Ryan revives his proposal from last year that would refashion Medicare, the government health insurance plan for the elderly, into a program that gives vouchers that can be used to buy private health insurance.

Ryan’s change would apply to people under 55. The program currently provides coverage directly to those 65 and older, although seniors have to pay premiums to the government to help finance the coverage.

Ryan’s proposal also would cut domestic programs including Medicaid, food stamps, agriculture and transportation, but provided few details. It repeals the federal health reform law passed in 2010.

Ryan introduced a similar plan last year, and Rehberg was one of only four House Republicans to vote against it, saying he wasn’t thrilled by the Medicare plan.

On Tuesday, Rehberg noted that vote and said he opposed the 2010 health reform law because it cuts nearly $500 billion in Medicare spending over 10 years, to help pay for new programs.

“One of the major problems with the Obama health care plan was nobody backing the plan took the time to ask Montana seniors before voting to cut $500 billion from Medicare,” he says. “And that’s why any plan to change Medicare will have to get support from Montana’s seniors first, or it won’t get my vote.”