WASHINGTON — Justice Kennedy told Congress yesterday that first-rate federal judges are leaving because of inadequate pay, a problem he said hurts morale and threatens to undermine judicial independence.

Earnings at private law firms have outpaced judges’ pay for many years, and Justice Kennedy said judges now find better compensation at the leading law schools, as well.

“I’m losing my best judges,” he said during a hearing of the Senate Judiciary Committee. He specifically cited U.S. District Judge David Levi, who is leaving as the chief federal judge in Sacramento, Calif., to become dean of Duke University’s law school.

Justice Kennedy worries that new judges, on the whole, are less qualified than the judges they are replacing.

Federal district court judges are paid $165,200 annually; appeals court judges make $175,100; associate justices of the Supreme Court earn $203,000; the chief justice gets $212,100.

Those figures are far less than what lawyers at private firms earn. District judges are paid about half that of deans and senior law professors at top schools.

Justice Kennedy said “$160,000 sounds like a lot of money to the average American, and it is. But it is insufficient to attract the finest members of the practicing bar to the bench.”

Nineteen federal judges left their jobs since the end of 2004, many of them to take higher-paying jobs. Meanwhile, first-year lawyers at leading firms in large cities are earning almost as much as district judges.

Chief Justice Roberts has made judges’ pay the centerpiece of his efforts as head of the federal judiciary, calling the issue a “constitutional crisis.”

Justice Kennedy got a sympathetic reaction from Senator Leahy, a Democrat of Vermont, the committee chairman, and Senator Specter, a Republican of Pennsylvania, who is the senior Republican. The Senate has passed a bill they wrote this year that would boost judges’ salaries to keep pace with the rate of inflation.

Legislation languished in Congress in 2006 that would have provided a 16% increase in federal judges’ salaries.

But other senators suggested that judges already are handsomely compensated.

Senator Durbin, a Democrat of Illinois, told Justice Kennedy he recognized the lure of large paychecks was driving some judges into private firms, but he noted that judges already earn more than 95% of the population.

Former Federal Reserve Chairman Paul Volcker recently called for a significant pay raise for judges, pointing out that they would be earning $261,000 a year if their salaries had risen at the same pace as American workers generally since 1969.