Transportation Secretary Elaine Chao and Democrats on the Senate Environment and Public Works Committee sparred Thursday over environmental requirements and funding in the president’s infrastructure proposal, jousting over the contents of a plan that top Senate Republicans indicated this week isn’t likely to pass this year.

Chao repeatedly defended the plan from charges by committee Democrats that it would strip environmental protections, saying the administration only wanted to improve the process without sacrificing environmental quality. The administration wants to eliminate duplication and allow relevant agencies to conduct environmental reviews simultaneously rather than sequentially, she said.

“We have no intent of diluting any environmental protection,” Chao said. “But if you look at the bureaucratic way in which permitting occurs, a lot of it doesn’t make sense. They’re redundant, they’re duplicative, they replicate one another, they discourage communications among sister agencies. There are many, many ways in which the permitting process can be improved without sacrificing environmental quality.”

The hearing marked the first time an administration official involved in the infrastructure plan took questions from lawmakers since the White House released the proposal Feb. 12. The proposal would provide $200 billion in federal spending over 10 years in an effort to spur $1.5 trillion in spending from all levels of government and the private sector. It encompasses not just transportation infrastructure but also energy, water and wastewater, and broadband.

Sen. Edward J. Markey, D-Mass., attacked the plan for relying on private-sector dollars — including through tolls or other additional user charges — while rolling back environmental regulations.

“If there isn’t a fundamental change that’s made, then citizens are going to end up with their environmental protections being watered down,” Markey said. “And they’re going to be tipped upside down, having money taken out of their pockets to pay for the fees.”

Senate Majority Whip John Cornyn, R-Texas., and Senate Commerce, Science and Transportation Chairman John Thune, R-S.D., said Tuesday it would be challenging for the Senate to pass an infrastructure bill this year. They said the schedule doesn’t have room for such a project.

Sen. Dan Sullivan, R-Alaska, a member of the Environment and Public Works Committee, said Thursday that lawmakers should find time to complete the legislation.

“We should make more time,” Sullivan said. “Let’s work weekends. Every American believes this is a priority.”

Democrats focused their criticism on the details of the plan.

Ranking member Thomas R. Carper, D-Del., said the administration is proposing to cut some areas of infrastructure and that the plan would — at best — shuffle federal money from one program to another.

Chao said the initiative would provide funding above and beyond current programs. She was evasive, though, about funding for the Highway Trust Fund, the source of funds for federal highway and transit formula programs that is projected to run out of money after fiscal 2020. Federal taxes on gasoline and diesel are the sources of revenue for trust fund, but they haven’t been raised since 1993, contributing to the insolvency.

Sen. Chris Van Hollen, D-Md., pressed Chao on President Donald Trump’s view of a gas tax increase. Lawmakers who attended a White House meeting last month told reporters Trump supported a 25-cent a gallon increase to the tax. Chao said she wouldn’t divulge the content of private conversations.

“You’ll have to ask the White House,” she said.

Carper called for a national pilot program on a vehicle-miles-traveled system of supporting the trust fund. Such a system would capture revenue from electric and other highly fuel-efficient vehicles that pay little or nothing into the Highway Trust Fund.