Democrats on the Senate Judiciary Committee, stung by criticism that they are rubber-stamping candidates for the federal bench, are trying to slow down the rapid-fire approval of President Reagan's judicial nominees.

Democratic members are pressing committee Chairman Strom Thurmond (R-S.C.) to allow them more time to investigate the nominees and to make each respond to a questionnaire from the minority staff. This is necessary, they contend, because a number of recent judicial candidates are younger, less experienced and more ideological than those named in Reagan's first term.

"We have not given close enough scrutiny to these nominees," said Sen. Paul Simon (D-Ill.), the committee's leading Democrat on judicial candidates. "We have so many names coming at us so rapidly it becomes difficult for us to do the kind of intensive work that needs to be done."

The attempted slowdown is the latest tactical move in one of the most important, if least visible, ideological battles of the 99th Congress.

The Democrats are acutely aware that Reagan is in the process of naming a majority of the nation's 743 federal trial and appellate judges and that he is determined to fill the bench with conservatives.

Since they are loath to oppose a nominee solely on ideological grounds, the Democrats have trained their fire on other issues -- tors judicial nominations, said the Republicans are executing "a brilliant tactical strategy. When you speed them through, you preclude outside groups and senators' staffs from taking a good hard look at these candidates."

Critics say that the Republicans can also slow down the action when there is conservative opposition to a nominee, as in the case of CIA general counsel Stanley Sporkin.

Sporkin's nomination to the District Court here has been held up for more than 16 months, and the panel recently began closed hearings into allegations denied by Sporkin that he improperly intervened in a Justice Department investigation of a leak of classified CIA information.

The committee has a history of false starts. It had to reopen its hearings on the nominations of Edwin Meese III as attorney general and William Bradford Reynolds as associate attorney general after new allegations surfaced. But Biden, who played a key role in both cases, has largely stayed in the background on judicial nominations.

Thurmond has refused to allow use of the Democrats' questionnaire, which would require more details about nominees' finances and club memberships, and would inquire whether the White House has asked how they would rule on abortion or school prayer. The administration has denied applying such ideological "litmus tests."

Simon said, "I confess I'm concerned about the ideological tilt . . . but you get on awfully thin ground rejecting nominees on an ideological basis." He said the American Bar Association, which rates judicial nominees, "has to be a little more careful in its screening. We're getting too many nominees who are just squeaking through."

But the Republicans view the kind of allegations made against Kozinski -- that he had been an abusive boss and misled the committee about his record -- as an excuse for Democrats to try to keep qualified conservatives off the bench.

Thurmond called the allegations against Kozinski, 35, "the puniest, most nitpicking charges ever raised against a judicial nominee." Sen. Orrin G. Hatch (R-Utah) said the charges were "pushed by a . . . coalition whose avowed intent is to delay President Reagan's judicial appointments by whatever means they can contrive."

Liberal groups such as Alliance for Justice have long since identified the next controversial nominees, who include Jeff Sessions, the U.S. attorney in Mobile, Ala.; Sidney Fitzwater, a 32-year-old Texas judge, and Michael Horowitz, general counsel of the Office of Management and Budget.

Some of the strongest lobbying takes place when an ABA screening committee is considering a nominee. Recently, for example, administration officials persuaded the ABA committee to reconsider Lino A. Graglia, a University of Texas law professor and outspoken opponent of school busing whom the panel had voted to reject.