WASHINGTON — Ending years of last-minute fixes, President Barack Obama on Thursday signed legislation permanently changing how Medicare pays doctors, a rare bipartisan achievement by Democrats and Republicans.

The bill overhauls a 1997 law that aimed to slow Medicare’s growth by limiting reimbursements to doctors. Instead, doctors threatened to leave the Medicare program, and that forced Congress repeatedly to block those reductions.

Obama signed the legislation in front of reporters. The Senate passed the bill two days ago; the House approved it in March.

He said the new law helps Medicare by giving assurance to doctors about their payments.

“It also improves it because it starts encouraging payments based on quality, not the number of tests that are provided or the number of procedures that are applied but whether or not people actually start feeling better,” Obama said. “It encourages us to continue to make the system better without denying service.”

The bill blocked a 21 percent cut in Medicare payments that was due to take effect this month. It also revamps how physicians will be paid in the future, by providing financial incentives for physicians to bill Medicare patients for their overall care.

Noting the unusual bipartisan nature of the bill, Obama said, “I hope this becomes a habit.”