Washington ? When it works, and if it works, the James Webb Space Telescope could revolutionize astronomy by peering so deep into space that scientists soon could study the dawn of time.

But construction of NASA’s next big telescope has been so hurt by delays and cost overruns that even its staunchest champion in Congress reached a breaking point.

In a letter dated June 29, U.S. Sen. Barbara Mikulski, D-Md., all but ordered NASA Administrator Charlie Bolden to assemble a panel of outside experts to ensure the Webb project doesn’t break its latest promise: a 2014 launch on a $5 billion budget.

“We like the concept of the Webb, but I tell you, we’re not in the overrun business,” said Mikulski, who chairs the Senate subcommittee with oversight of NASA’s budget.

NASA agreed to form the panel and placed veteran engineer John Casani in charge.

Even so, keeping the Webb on track won’t be easy. Already, the telescope is at least $1.5 billion over budget and three years behind schedule, thanks to poor financial planning and knotty engineering problems, according to government watchdogs.

And further delays and cost overruns are possible. Just last year, Mikulski had to secure an additional $75 million to keep Webb workers on the job as part of the $862 billion stimulus plan passed by congressional Democrats.

The budget-busting hasn’t happened in a vacuum either.

An upcoming report from the National Academies is expected to underscore concerns that American astronomy doesn’t get the funding it needs — a situation exacerbated by the Webb telescope.

“When Webb bleeds, the rest of space science hemorrhages,” said Michael Turner, one of the report’s authors and a professor of astronomy and astrophysics at the University of Chicago.

Smaller robotic missions have suffered because of cost overruns with Webb, Turner said. But the project has been kept alive by expectations about what it can do and the need to replace the popular Hubble Space Telescope, which could end operations as early as 2014.

“It’s been a long wait, and it’s been very expensive. But when it is launched and operating, people are going to forget the wait and how much it cost, and they are going to go gaga about the discoveries,” he said.

It can take billions of years for the light of distant stars to reach Earth. As designed, the Webb can see so far into space that it essentially can look back in time.

This quirk in physics will enable Webb scientists to learn more about the events that immediately followed the big bang, a cosmic explosion that scientists think created the universe more than 13 billion years ago.

“We are aiming to see the realm between 250 million years after the big bang to about 400 million years afterward,” said Jonathan Gardner, a top Webb scientist. Hubble can only see within 800 million years of the big bang.

“The James Webb is designed to find the first galaxies that formed in the early universe,” Gardner said.