WASHINGTON – Judges who have been nominated to appellate courts by President Bush face confirmation delays almost three times as long as judges nominated for the same jobs by his father, President George H.W. Bush, a new study shows.

The lags in confirmations have been growing longer with each successive administration, and accelerated after Republicans took control of Congress under President Clinton, says a lengthy review of judicial confirmations by a scholar at the American Enterprise Institute, John Lott.

The wide-ranging statistical analysis is sure to add new fodder to the Senate battle over judicial nominations as Republicans edge closer to changing Senate rules and end the ability of Democrats to delay floor votes on the nominees.

The study makes the provocative claim that the most productive and frequently cited judges – whom Mr. Lott labels “quality” judges – are taking the longest to be confirmed. His results raise the question of whether the cumbersome and divisive process is affecting the quality of the bench.

“You are having a reduction in the actual effectiveness of the judges on the bench over time. That is a possible real cost of the more dragged-out fights we’ve been having,” Mr. Lott said in an interview.

Mr. Lott speculated that Democrats target their opposition to block smart judges who are likely to be influential. It is a claim that was quickly rejected by at least one Democrat who has read the study.

“People are not being opposed because they are smart,” said a former White House counsel to Mr. Clinton, William Marshall. “People are being opposed because the Bush administration is trying to effectuate an ideological agenda,” said Mr. Marshall, a professor of law at the University of North Carolina at Chapel Hill.

The study also probes claims made by Senator Schumer and other Democrats that they are wrongfully labeled obstructionist, because in Mr. Bush’s first term they approved 204 judges and turned down 10. Those numbers do not tell the full story, because the tally does not include the 15 judges who were blocked from reaching a vote on the Senate floor, Mr. Lott noted. More importantly, he argued, the number lumps together district and circuit court judges, obscuring what he finds to be a dramatically lower confirmation rate for the appellate judges.

“What is happening with district court judges is being use to mask what is happening to most important nominees,” he said.

The study of 297 federal judicial appointments from 1977 through the end of 2004 concludes that neither party has clean hands in the battle, which has escalated dramatically in recent years.

Nominees had the greatest delays when the opposition party controlled Congress, Mr. Lott found.

By the beginning of the Bush administration, circuit court nominees had to wait twice as long – 320 days on average – than in the last two years of the Clinton administration.

“Not only is the confirmation process getting longer, but the confirmation rates have been declining precipitously,” said Mr. Lott.

The length of the confirmation process, for both district and circuit court nominees, was around 50 days starting with the Carter administration through the first six years of the Reagan administration, he found.

But the time taken more than doubled when the Democrats took over the Senate and battled Judge Robert Bork’s nomination to the Supreme Court in 1987.

For the next decade, the new average was 120 days. It was ratcheted up again during the last four years of the Clinton administration and into the administration of the current president.

The findings are consistent with past studies on the subject, said a professor of law at George Mason University, Todd Zywicki, who was read the paper.

“We have moved from a presumption of confirmation to the presumption of obstruction,” he said.

The paper’s most important contribution is highlighting the dramatically different treatment of various nominees to the appellate courts, who have the power to overrule lower court opinions and are seen as potential candidates to the Supreme Court, Mr. Zywicki said.

The confirmation rate for district court nominees during the 2003-04 term was virtually the same as in 1977-78. In contrast, the confirmation rate for appellate judges hovered between 92% to 100% from 1977 to 1986,but fell below 82% after the first two years of the Clinton administration. During the last two years of his administration, the rate fell to 74%.

It fell again to 64% during Mr. Bush’s first administration, Mr. Lott found.

Mr. Lott, who has served as chief economist to the federal Sentencing Commission, and has been a fellow at the law schools of the University of Chicago and Yale, used mathematical modeling to test the impact of a variety of factors on the length and odds of the nominees’ confirmation.

One potentially contentious finding of the paper is the claim that Mr. Bush’s nominees are no more ideological then were those of his father or President Reagan. Mr. Lott concludes that the ideology of the senators, and not the judges, is contributing to the delays.

“What is happening is Congress is becoming more ideologically polarized,” he said.

But the former Clinton official, Mr. Marshall, denied that Democrats are being more obstructionist than were Republicans under Mr. Clinton.

Mr. Marshall notes that the study does not include many of the judges that Mr. Bush has nominated but who have been delayed from being voted on in the Senate.

“What has skewed the statistics here is the particular group of judges that the Democrats have found to be ideologically rigid,” he said. Mr. Clinton consulted with Republicans on some appointments and received more cooperation as a result, he added.

Dispelling past claims of racial and gender discrimination against Clinton nominees, Mr. Lott found that Mr. Bush’s female and black nominees took even longer to be confirmed. He did not find any general patterns of discrimination.

Another aspect of the study that is likely to generate controversy is his assertion that the quality of judges is unrelated to their professional qualification rating from the American Bar Association, or the prestige of the law school they attended. Mr. Lott’s measure of quality is based on 16 measures used by other law professors, including such variables as output of decisions and frequency of being cited by other judges.

Mr. Zywicki cautioned that the measures are not straightforward, but he said the study will cause the legal community to question the association’s ratings.

Officials at the ABA had not read the study and were not able to comment yesterday.