There is a new Philadelphia these days. A federal one.

Philadelphia is where Mayor Marion Barry would call to find out why the city's summer youth program money is late. Philadelphia is where a Cleveland Park widow would write for Social Security benefits. Philadephia is where one can walk the federal halls and overhear people discussing job training programs for Anacostia. . . . Money for lead-based paint safety programs . . . housing grants . . . income tax refunds: This is the place for them all.

"Simply put," says Dr. H. McDonald Rimple, regional adminstrator of the U.S. Public Health Service, "Philadelphia is where the rubber meets the road."

More formally, it is headquarters for the federal government's Region III.

The region was established-and Philadephia chosen as its headquarters-10 years ago by President Richard M. Nixon. The idea was to spread the federal presence beyond the District of Columbia, but gather branches of the major federal agencies in one Middle Atlantic city.

Region III encompasses Pennsylvania, Delaware, Maryland, Virginia, West Virginia and the District. One of 10 such regions in the country, Region III is the third largest in terms of funds administered and population served. In addition, more than 400 federal employees here are former Washingtonians.

More than $4 billion is being administered in Philadelphia this fiscal year, by more than 18,000 federal employes, at more than a dozen major agencies. Every federal dollar spent in the Middle Atlantic states tis fiscal year will have been approved, administered or reviewed in a federal office in Philadephia-and often all three. The Washington metropolitan area alone will receive nearly $750 million in grants, loans and administrative attention from Philadelphia this fiscal year.

Philadelphia, the city, has never had an identity crisis. W.C. Fields, Mayor Frank Rizzo and several heartrendingly awful sports teams have seen to that. But federal Philadelphia, Region III, continues to struggle for identity despite all its money, employes and power.

The foremost reason is that when Washingtonians picture the federal government's physical presence, they tend to think of limestone labyrinths in South-West a post office, a military base-anything but office buildings in downtown Philadelphia.

Even Philadelphians seem unaware that theirs is an increasingly federal city.

As proof of sorts, a reporter stood on Market Street one recent weekday evening at rush hour, a block from the Curtis Building (Environmental Protection Agency and Housing and Urban Development) and less than three miles from the Gateway Building (Health, Education and Welfare and Labor and Commerce). He asked 25 persons two questions each: Where are the federal government's offices in Philadelphia? and, What do the initials HEW stand for?

The tally was 0-for-50.

The second reason for federal identity trouble here is that an uncanny number of top federal officials in Philadelphia have previously served Uncle Sam in Washington.

Interviews with more than a dozen of those officials indicate that they do not miss what one called "the Washington fishbowl." Nor do any feel that the move to Philadelphia has been a step down professionally.

But all officials say that their experience in Washington has made them more aware of what Stephanie Naidoff, HEW's 37-year-old regional attorney, calls "the stepchild syndrome."

Naidoff moved to Philadelphia and Region III six years ago. With her she brought a son, a husband who decided to open his medical practice in Philadelphia - "and the notion that federal employment might not be as challenging, exciting and glamorous as Washington.

"You know the fountainhead theory-that it all flows from Washington. When I worked there, I sensed the attitude. They just tolerated regional offices," said Naidoff, who was special assistant to the HEW general counsel while in Washington.

She is now convinced that, in Philadelphia, "there's the best of both worlds. It's not a company town. Everybody's perspective doesn't revolve around what the government is doing. Philadelphia is part of the larger world, and I don't mean that to be self-serving. It makes for better work and better workers.

"But I'm still not sure Washington knows that."

Mac Rimple said he "tended to look on regional offices as an outpost" when he was working at the Parklawn Building in Rockville, as deputy director of the Public Health Service's bureau of medical services.

"But what I've found since my promotion here is that regional offices not only contain employes who are knowledgable as to programs, but they have an added dimension: They understand the nuances between states that we in the central office knew about but didn't quite grasp or appreciate."

Lois Blechl, who heads federal certification for the hiring of alien workers, spent 13 years at Labor Department headquarters in Washington. She says she will always be sentimentally attached to Washington, since she and her husband met at a country-and-western bar in Southeast (he was a part-time bar-tender, she a part-time customer). But she transferred to Region III 10 years ago to be nearer to her family in Pennsauken, N.J.

Blechl said she often privately compares the two cities as places for a federal employe to work. She always picks Philadelphia.

"I don't think there's quite as much political pressure here," said Blechl, who is 40. "You're not on public display here. In D.C., the Shah of Iran would come through one day, Alan Shepard the next, Up here, those things don't happen."

Andrelia (Nady) James, a 30-year-old GS-9 equal employment opportunity officer for the office of human development in HEW, said that in terms of opportunity for black and female federal workers, Philadelphia outdoes Washington in some ways and trails it in others.

"It's so open here. There's so many positions available," said James, a Washington native and Spingarn High School graduate who transferred to Philadelphia five years ago to follow her new husband and his dry cleaning business to nearby Norristown, Pa.

" But there's a difference in attitude, too. Region III is run by white males who expect to keep on running it. Most of the vacancies for minorities and women are on the bottom.

"We can get people in the door, probably better than in D.C. Hey, Andy James is doing pretty good, pretty good. But if you're just sitting down in the mailroom shooting darts, you're not being effective, I don't think."

Whether Philadelphia's location helps its effectiveness as Region III headquarters is another frequent question here.

Philadelphia is as far east, and nearly as far north, as one can get in Region III. The taxpayers thus subsidize travel costs that are as high as they could be. In addition, to get to any location in Virginia or West Virginia-as they must do regularly-Region III employes must travel through Washington or Pittsburgh.

Wouldn't it thus make sense for Region III headquarters to be in Washington or Pittsburgh, or a more centrally located city, such as Baltimore, Hagerstown or Frederick? "In terms of georgraphy," says Greene Jones, water programs division director at EPA, "you'd have to say it would."

But Philadelphia gives employes one "sneaky" advantage-the two hours it takes to get to Washington, the most frequent travel destination, on Amtrak's Metroliner.

"I live for that time," said Rimple. "You can work on the train, and I always do."

"It's the only time I can get through the mail," added Harry Staller, HUD's deputy regional adminstrator, who headed HUD's Washington area office until his promotion two years ago.

Region III headquarters is a more formal place to work than federal Washington in some ways, less formal in others.

Several elevators are still run by elderly men who wear well-pressed maroon uniforms and carefully call out the floors. Where it says "No Smoking," people don't. And almost none of the male employes comes to work in anything less than jackets and ties.

"Up here, I felt, if you're going to be a chemist, you've got to look like one," said Charles Jones Jr., who is one for the EPA.

But secretaries at Region III tend to call their bosses Bill and Fred, rather than Mr. Johnson or Mr. Smith. People of either sex fetch coffee. And record-keeping of annual leave is not nearly so devout as in Washington. "If someone has a sick kid, they go - and no one says a thing," said an HEW secretary.

A subtle aspect of being a "fed" in Philadelphia is the way in which one introduces oneself to non-feds.

Stephanie Naidoff, for instance, replies, "I'm an attorney" in Philadelphia. In Washington, she used to say, "I work at HEW." Why the change? "It's the post-Watergate memtality, I guess. People don't think government employes wear white hats."

The paramount question about Region III, however, is whether it works. Unanimously, congressional, state, local and federal officials say its does. And President Carter is on record as favoring the regional approach.

"I have no doubt the regional concept is here to stay," said Greene Jones.

But couldn't a centralized staff in Washington do the job as well?

"Emphatically not," Jones said.

"Regional concerns would be swallowed up if we were in Washington, under the shadow of the whole federal government," added Staller.

"Every state and problem we deal with has a unique character," said Jones. "It's our job to know them better than Washington ever could. It's not a question of major league and minor league-it's a different ball game." CAPTION: Illustration, no captian, By Annie Lunsford for The Washington Post; Picture 1, H. McDonald Rimple, Public Health Service regional administrator, calls it the place where "rubber meets the road." By Dan Miller for The Washington Post; Picture 2, Andrelia James of HEW: "It's so open here."; Picture 3, Stephanie Naidoff, HEW's regional attorney.