His name is never mentioned in talk about who's who in the Carter administration. In fact, anyone trying to pinpoint where he stands in the pecking order would have to look extra hard to find him on the organization charts.

But that hasn't stopped a 50-year-old Georgia Republican named Michael J. Egan from quietly assuming an increasingly large role in the government of a President he knows as "my old friend Jimmy."

Egan's base is in the Justice Department, where he holds the post of associate attorney general. Despite the title, that's supposed to be a staff trouble-shooting job rather than a part of the department's chain of command. It's not even among the 11 Justice Department positions whose occupations must be confirmed by the Senate.

However, Egan, is, in fact if not in title, the second-in-command to Attorney General Griffin B. Bell. In terms of ability to influence those department activities with the biggest impact on public policy, no other Bell subordinate - including Deputy Attorney General Peter F. Flaherty - has more clout.

That was made clear by Bell in a memorandum he recently sent to department executives. Its effect was to make Egan the de factor No. 2 man by assigning him many of the most important powers traditionally exercised by the deputy attorney general.

Eventually, Bell has made clear, he plans to ask Congress for legislation that will "legalize" this situation by creating a second deputy attorney general position. In the meantime, though, the Justice Department is operating under a system that has most of its division heads taking orders from a man in a technically subordinate office.

That's a situation with some potentially sensitive implications, and Bell and Egan have gone out of their way to avoid giving the impression that Flaherty, the highly visible former mayer of Pittsburgh, is just a figurehead around the department.

In Bell's absence, it's Flaherty who takes over as acting attorney general, as required by law. Under the realignment of functions, Flaherty also retains control over criminal investigations and prosecutions - that aspect of Justice Department activity most familiar to the press and public.

That gives Flaherty supervision of the Criminal Division, which prosecutes most cases involving violations of federal law, and those federal police agencies under the authority of the Justice Department: the FBI, the Law Enforcement Assistance Administration, the Drug Enforcement Administration, the Bureau of Prisons and the Federal Marshals Service.

Since these organzations jointly account for the biggest share of Justice Department personnel and budget appropriations. Flaherty's jurisdiction covers almost 40,000 people and $2 billion. By contrast, Egan likes to point out, the activities under his control involve only 12,000 people and $339 million.

However, in the Justice Department's scheme of things, command over men and money isn't necessarily the true test of power. As lawyers and politicians are aware, those divisions of the department most capable of affecting the nation's economic, social and political structure operate in the field of civil, rather than criminal law.

These are the divison - Civil, Civil Rights, Tax, Antitrust, Land and Nature Resources - that have been placed under Egan's control. As a result, it is Egan who will have the biggest influence in advising Bell and the President on a broad range of key policy issues involving everything from the busing of school children to possible legislation aimed at breaking up big companies in the energy field.

Of course, Egan won't be the only person involved in such decisions. But his authority to order the priorities of these divisions, to ride hard on the work done by their staff attorneys and to approve or disapprove the recommendations that they send up will have great effect on the policy proposals that ultimately land on the Attorney General's desk.

Since Bell's team is only newly in place, it hasn't yet projected any clean-cut image of how it will approach the various legal issues facing the administration. Career Justice Department employees say that, while they don't yet have a really clear idea of Egan's political and legal philosophy, the evidence so far seems to support Egan's reputation back home in Georgia as an exemplar of moderate, "New South" Republicanism.

Also included in Egan's turf are the considerate patronage powers at the disposal of the Justice Department. He is the man who, in the delicate phrasing of Bell's memo, "prepares recommendations" for appointment to federal judgeships and U.S. attorney positions and who "has final authority" over all department personnel actions from "supergrade appointments" to the recruitment of law school graduates.

Perhaps most significantly of all, Bell's memo designated Egan as the man who "coordinates departmental liaison with the White House staff and the executive office of the President."

That's a lot of responsibility for someone holding an office that originally was created during the tenure of former Attorney General Elliot L. Richardson to house a staff aide who wasn't even a lawyer and that has left vacant by the last two Attorneys General.

However, finding himself in an anomalous situation isn't a new experience for Egan, an Altanta attorney who rose to considerable influence in the Georgia power structure despite being a Catholic and a Republican in a Baptist and Democratic state.

Egan's route to Washington ran through the Georgia legislature, where he served as minority leader from 1971 until early this year. In the early '70s, he forged an alliance with then Gov. Jimmy Carter, who was feuding with the legislature's Democratic majority, and Carter has said that he owned enactment of many of his programs to the Republican support rounded up by Egan.

After the election returns were in last November, Egan sat down and wrote what he describes as "the last letter in which I used the saluation 'Dear Jimmy.'" In it, he says, "I told him that if I could help him out in any way in Washington to let me know."TEgan claims that he doesn't know what happened next. But the evidence suggests strongly that Carter did some whispering in the ear of Bell, who also was a prominent Atlanta lawyer. At any rate, one of Bell's very first acts after being named Attorney General was to call Egan and tell him that he was being signed on as his right-hand man.

Despite their common Georgia origins, the two seem outwardly an oddly matched pair. Bell, with his drawl and his fondness for folksy, country-boy aphorisms, already has become famous in Washington as a central-easting prototype of the foxy, backwoods lawyer. By contrast, Egan projects an air of smooth-as-glass sophistication that some say is characteristic of his hometown, Georgia's cosmopolitan port city of Savannah.

Still, the two have worked together like the main cogs in a piece of carefully calibrated precision machinery. From the moment of their arrival in Washington, Bell began delegating so much responsibility to Egan that "Clear it with Mike" quickly became one of the most frequently heard phrases around the Justice Department.

Inevitably, the expanding of Egan's authority has started to peel away some of his anonymity; and there have been a few rumblings from Capitol Hill about the propriety of so much power being exercised by someone in an ostensibly lowly office.

Some senators and Hill staffers say privately that if Carter and Bell want Egan to function as he's been doing, they should put him in a position that requires the scrutiny of confirmation by the Senate.

According to what Justice Department sources say is Bell's tentative plan, that probably won't happen until next year. Wen the Carter administration goes to Congress with its proposal for an across-the-board governmental reorganization, it will include a request that the deputy attorney general's slot be split into two positions.

Egan adds: "That doesn't mean that there's a squatter's right clause attached to the job. Even if Congress goes along with the request, I have no guarantee or even an inkling that I'll be the man whom the President nominates for the job."

Given the record so far, though, no one in the Justice Department seems to have any doubts that, whatever the reorganization that ultimately takes place, they'll be hearing "Clear it with Mike" for some time to come.