At his Feb. 23 press conference President Carter repeated a persistent pledge: "I will do my utmost to keep all the campaign promises that I made to the American people."

But all his reaffirmation haven't shielded Carter from charges that he has retreated from one of the most important of his campaign promises - a merit system for the selection of federal judges and prosecutors.

So far, the efforts made by his administration to redeem tht pledge seem to have caused mainly disillusionment among advocates of political and legal reform.

Their unhappiness was summarized recently by David Cohen, president of Common Cause, who told the Senate Judiciary Committee: "President Carter's disappointing action is a far cry from candidate Carter's pledges."

That is disputed by the Carter appointees now at the Justice Department. They contend that the new administration already has done more to reform the selection system than any previous President.

Still, they concede that what has been dojne falls far short of the position set forth by Carter in the campaign. It said:

"All federal judges and prosecutors should be appointed strictly on the basis of merit without any consideration of political aspects or influence. Independent blue ribbon judicial selectlion committees should be established to give recommendations to the President of the most qualified persons available for positions when vacancies occur."

It was a classic example of campaign rhetoric totally out of step with political reality. Even before they arrived in Washington, the Carter people knew there was no chance for a wholesale rewriting of the rules by which the game traditionally has been played.

Under the system that has evolved over the years, the senators from the Prsident's party have almost unlimited power to pick, or at least veto, any federal judges maned in their states. Without the approval of the senator involved, there is virtually no chance of a judicial nominee gaining the necessary Senate confirmation.

Nor is the Senate likely to relinquish this power at a time when the patronage possibilities in the federal judiciary are about to increase significantly. It seems almost certain that Congress soon will vote to increase the present quota of 383 U.S District court by judges by as many of 106.

When that number is added to existing vacancies, Carter could be in the position of naming up to 122 new district court judges - more at one time than any previous President. Under those circumstances, few senators would be willing to surrender their influence over his choices.

That is why the administration never tried to institute the selection system proposed by Carter in the campaign. As the new Attorney General, Griffin B. Bell, bluntly puts it: "We can't just issue an order and say this is the way it's going to be.

We'd get a lot of publicity, but we wouldn't get any judges.

Still, Bell's new Justice Department team insists that the president's pledge hasn't been forgotten. While conceding that there's no chance for overnight reform, officials are working on a program of gradual change and persuasion that they hope will evolve eventually into a full-fledged merit system.

The outlines of this plan have been drawn by Bell and a Georgia Republican named Michael J. Egan, whom Carter has installed at justice as associate attorney general. Egan, a former minority leader of the Georgia legislature, worked closely with then Govt. Carter to set up a merit system for Georgia state judgeships.

The plan calls for setting up three separate systems - for U.S. district court judges and U.S. attorneys - each carefully calibrated to the political consideration attaching to these categories.

The plan covering circuit courts come closest to Carter's original promise, because these courts have jurisdictions spreading across several states: and it's harder for individual senators to exercise decisive influence over the appointments.

An executive order issued by Carter Feb. 15 has established 13 advisory panels, each covering all or part of the 11 appellate court circuits, to recommend prospective nominees for vacancies. Egan says thes panels will be "roughly half lawyers and half non-lawyers" and will give representation to minorities, women and other groups that have complained of being frozen out of the judicial selection process in the past.

When a vacancy occurs, the appropriate panel will give Carter a list of the five persons it considers best qualified for appointment. While these recommendations are not binding Egan says it is "virtually certain" that the President, after further checking with groups like the American Bar Association and the largely black National Bar Association, will choose his nominees from the five-person lists.

However, the "track" for picking district court judges is so solicitors of senatorial prerogatives that Common Cause's Cohen dismisses it as "not even a first step toward merit selection.

Essentially, it leaves intact the power of senators to pick the judges in their states. But it tried to persuade them to make their choices on a merit basis by setting up their own advisory panels or other consultative machinery within their respective states.

So far, the senators from six states - Florida, Kentucky, California, Iowa, Massachusetts and Georgia - have agreed to let local commissions guide their choices for district judgeships. The hope, Egan says, is that the idea will spread and eventually embrace all 50 states.

"We don't say there has to be a uniform system in each state," he notes. "In Illinois, for example, Sen. (Charles H.) Percy, who's a Republican, has been using a method of consulting informally but intensively with a broad soectrum of groups before deciding on his recommendations for district court vacancies. The important thing is not the specific method, but its effectiveness in producing candidates who are the best qualified."

However, six states are still only a small fraction of 50. And, the critics, recalling that last year Sen. William L. Scott (R-Va) blocked the nomination of a high qualified lawyer, William B. Poff, for arbitrary personal reasons, think Egan is being somewhat distingenous in asserting that the idea is likely to be embraced with a speed or enthusiasm by 100 different senators.

A roughly comparable approach is being applied to U.S. attorneys - in many respects the most politically sensitive of the three categories.

For example, the new Republican governor of Illinois, James Thompson rode into office on the strength of his success in prosecuting members of Chicago's Democratic machine.The task could have been more difficult under a Democratic President - at least while Chicago's late Mayor Richard J. Daley was an important force in his party.

Egans says the Carter administration wants the merit principle applied to U.S. attorneys: and Bell has said that all Republican appointees who want to stay will considered for retention on that basis. But Bell also has made clear that the opinions of senators and other political leaders in the areas involved will be listened to carefully and that, in cases of close calls, Democrats will have an edge over Republicans.

Some career Justice Department official predicted that the U.S. attorney appointments, even more than the judgeships, will provide the best clue to how hard the Carter administration will fight against political pressures that Carter will have to make won't all be as easy as the free pass he recently got in New York.

That state has three Republican appointed U.S. attorneys, all with reputations for high-grade job performance. The protest that would have been caused by their ouster was averted when New York's new Democrativ senator, Daniel P. Moynihan, unexpectedly announced that he wanted them kept in office.

Carter also will be able to slide past some other potentially tricky situations, such as Chicago where the incumbent Republican appointee, Samuel Skinner, has woh high marks from the legal community. Sen. Adlai E. Stevenson (D-III), who wants him replaced, has been careful to come up with a candidate, Thomas P. Sullivan, whose credentials are impecably nonpartisan.

As a result, Egan shows no apparent discomfiture in staying: "Sam Skinner is a very good man who has the support and trust of the department. He's the kind of incumbent we want to keep. Still, it's hard to say what's going to happen when Stevenson has found a man who seem so highly qualified.

Sooner or later though. Carter will face a decision that hinges on a choice between merit and political clout. Some Justice Department sources say the potentially most revealing test will come in New Jersey.

There, a succession of Republican appointed U.S. attorneys have won national prominences for their non-partisan assaults on the links between politicans and organized crime. For that reason, the present occupant of the office, Jonathan Goldstein, is being strongly supported for retention by the state's legal and law enforcement establishments.

However, there are powerful forces in the New Jersay Democratic Party who want him out.Sen. Harrison A. Williams Jr. (D-N.J.) has hinted that Goldstein should be replaced by someone more to his, and the party's liking.