A senior Democratic senator who helped write President Barack Obama’s health care law stunned administration officials Wednesday, saying openly he thinks it’s headed for a “train wreck” because of bumbling implementation.

“I just see a huge train wreck coming down,” Senate Finance Committee Chairman Max Baucus, D-Mont., told Obama’s health care chief during a routine budget hearing that suddenly turned tense.

Baucus is the first top Democrat to publicly voice fears about the rollout of the new health care law, designed to bring coverage to some 30 million uninsured Americans through a mix of government programs and tax credits for private insurance, starting next year. Polls show the public remains confused by the complexity of the law, and even many uninsured people are skeptical that they will be helped.

A six-term senator, Baucus expects to face a tough re-election campaign in 2014. He’s still trying to recover from approval ratings that nosedived amid displeasure with the health care law in his home state.

Normally low-key and supportive, Baucus challenged Health and Human Services Secretary Kathleen Sebelius at Wednesday’s hearing.

He said he’s “very concerned” that new health insurance marketplaces for consumers and small businesses will not open on time in every state, and that if they do, they might just flop because residents don’t have the information they need to make choices.

“The administration’s public information campaign on the benefits of the Affordable Care Act deserves a failing grade,” he told Sebelius. “You need to fix this.”

Responding to Baucus, Sebelius pointedly noted that Republicans in Congress last year blocked funding for carrying out the health care law, and she had to resort to raiding other departmental funds that were legally available to her.

The administration is asking for $1.5 billion in next year’s budget, and Republicans don’t seem willing to grant that, either.

At one point, as Sebelius tried to answer Baucus’ demand for facts and figures, the senator admonished: “You haven’t given me any data; you just give me concepts, frankly.”

“I don’t know what he’s looking at,” Sebelius told reporters following her out of the room after Baucus adjourned the hearing. “But we are on track to fully implement marketplaces in January 2014, and to be open for open enrollment.”

That open-enrollment launch is only months away: Oct. 1. It’s when millions of middle-class consumers who don’t get coverage through their jobs will be able to start shopping for a private plan in the new marketplaces, or exchanges. They will also be able to find out if they qualify for tax credits that will lower their premiums. At the same time, low-income people will be steered to government programs, mainly an expanded version of Medicaid.

But half the states, most of them Republican-led, have refused to cooperate in setting up the infrastructure of Obama’s law. Others, like Montana, are politically divided.

The overhaul law provided that the federal government would step in and run the new markets if a state failed to do so. Envisioned as a fallback, federal control now looks like it will be the norm in about half the country, straining resources.

Administration officials say their public outreach campaign will begin in earnest over the summer. They question the wisdom of bombarding consumers with insurance details now, when there’s not yet anything to sign up for. Baucus said in his state, that vacuum has mostly been filled by misinformation.

While some other Democratic lawmakers have privately voiced similar frustrations, most have publicly lauded Sebelius for her department’s work.