A senior Republican senator whose involvement is key if there's going to be a bipartisan health care reform deal is responding angrily to President Barack Obama's latest comments on the issue.

Obama, after months of standing back and leaving the details of health care legislation to Congress, inserted himself firmly into the debate in recent days, including using his weekly radio address Saturday to declare "it's time to deliver" on health reform.

That did not sit well with the Sen. Chuck Grassley of Iowa, the top Republican on the Finance Committee, which has been laboring to come up with a health care bill that Democrats and Republicans can support.

Grassley is a frequent user of Twitter _ the Internet-based social connection service that allows users to send mass text messages called "tweets" _ and he directed two angry "tweets" Sunday morning at Obama. The president was wrapping up an overseas trip with some time to tour Paris with his family.

Grassley's first tweet: "Pres Obama you got nerve while u sightseeing in Paris to tell us 'time to deliver' on health care. We still on skedul/even workinWKEND."

A short time later: "Pres Obama while u sightseeing in Paris u said 'time to delivr on healthcare' When you are a 'hammer' u think evrything is NAIL I'm no NAIL."

A Grassley spokeswoman verified that Grassley was the author of the messages.

Asked to respond to Grassley's Twitter commentary, White House spokesman Reid Cherlin said: "President Obama is gratified that the Senate is working hard to bring a health reform bill to the floor on schedule. He looks forward to continuing his work with them upon his return from the commemoration of Allied heroism at D-Day."

Grassley's attitude is significant because any hope for bipartisan consensus on health care rests on an alliance between Grassley and Finance Committee Chairman Max Baucus, a Montana Democrat.

Despite strong opposition from most Republicans to one of Obama's key goals for a health care bill _ the inclusion of a new government insurance plan to compete with private insurers _ Baucus and Grassley have continued to hold out hope that they can find a solution that could garner bipartisan support.

Obama senior adviser David Axelrod cited Grassley in an interview on CBS television's "Face the Nation" Sunday morning as a reason there is hope for a health overhaul deal. Obama wants to sign legislation in the fall that would hold down costs and extend coverage to 50 million uninsured Americans.

"I would hope people of both parties would get together. I was encouraged by Sen. Grassley's comments in the last few days suggesting that he thought we could get there," Axelrod said. "So I think we'll be able to build a bipartisan support for it. But we have to move forward with it, I think it is a critical situation for the country and our economy and our future."

Obama has said repeatedly he wants a bipartisan bill. Although the Democratic-controlled Congress might be able to pass health care legislation with little or no Republican support, such a measure would be less widely accepted and less sustainable over time, Baucus and others have said.

But Obama's increased involvement appears to be diminishing chances for bipartisanship, not improving them. Grassley and other Republicans were also angered when Obama released a letter last week coming down strongly in favor of a new public insurance plan.

The next few weeks will be critical to the health care debate, with the Finance Committee to finalize legislation and begin voting in late June. Sen. Edward M. Kennedy's Health, Education, Labor and Pensions Committee has circulated draft legislation that is unlikely to garner Republican support because of the greatly expanded role it gives to government. The Finance Committee has been expected to produce a bill with a narrower role for government.