When the mayor's new chief of staff arrived in the summer of 2001, about 200 members of the political community welcomed him to town at a lavish reception at the home of Gwendolyn M. Hemphill, a woman with a knack for quietly placing herself at the crossroads of power.

She is now, 18 months later, at the crossroads of scandal. Hemphill is the link -- and for Mayor Anthony A. Williams, a deeply worrisome one -- between the nominating petition debacle that marred his reelection effort and the allegations of $5 million worth of misspending by officials of the Washington Teachers' Union, among the mayor's earliest and most avid supporters.

An FBI affidavit and a 65-page union audit portray Hemphill, who until October was the mayor's campaign co-chairman, as a brazen thief. She allegedly bought herself a $13,000 plasma television, wielded a signature stamp to convert union checks into cash and used a corporate American Express card to lavish luxuries on herself and family members. The audit puts Hemphill's misspending alone at more than $492,000 in goods and cash and says the total may be much higher. A grand jury, guided by two federal prosecutors, has subpoenaed union records, and authorities searched the homes of Hemphill and others last month. No charges have been filed.

But it is the earlier image of Hemphill, 61, as the savvy hostess, dishing out barbecued ribs and political gossip, that endures for many in the city's tight-knit political community. She was the kind of woman who, decade after decade, seemed at the right place at the right time as mayors came and went, helping to keep family members in government jobs but rarely drawing attention to herself as anything but an exceptionally eager political activist.

"I was astounded," said longtime friend and political activist Lawrence Guyot, speaking about the allegations against Hemphill. "Everything that I know about her was about service, about concern for other people. That's the Gwen Hemphill I knew."

Hemphill has a matronly manner and typically speaks slowly and softly. She has a long history of civic activism, including helping to start a program by the National Coalition of 100 Black Women to provide cribs and temporary homes for abandoned infants. And she was, in the union and its scandal, a secondary figure to her boss, president Barbara A. Bullock.

Yet in light of the growing list of allegations against Hemphill, her political associates, former co-workers and friends -- most of whom declined to be quoted by name because of the sensitive nature of the case -- are searching their memories for clues to Hemphill's alleged other side.

There are the cars, including a 1999 Mercedes-Benz E430 that bears a coveted low-numbered license plate, 14, issued by the mayor. There are the clothes and fancy handbags that seemed beyond the means of a woman with union and government jobs, even when her husband's government salary was factored in. There are the whiffs of financial trouble over the years, detailed in court and other records, which include a pair of tax liens, a 1986 bankruptcy and the use of a city emergency mortgage assistance fund in 1984, when she was a top government official.

And then there are the other mysteries, such as who paid for that party in Hemphill's back yard. Those who were there recall the scrumptious food, the band and the elegant setting in Colonial Village, nestled up to Rock Creek Park at the city's northern corner.

Hemphill declined to comment for this article. The guest of honor at the event, mayoral Chief of Staff Kelvin J. Robinson, said through a spokesman that he doesn't know who paid for the party. The audit and the FBI affidavit shed no light on it.

What those documents do allege are repeated episodes of Hemphill and other officials essentially treating the bank account of the Washington Teachers' Union as their own.

A lawsuit filed against Hemphill and others Thursday by the American Federation of Teachers, the parent of the Washington Teachers' Union, recaps many of the allegations outlined in the FBI affidavit. It alleges that Hemphill, whose union salary was $70,000 a year, used union credit cards to buy herself art, antiques, electronic equipment, jewelry, evening gowns, hair care, personal travel, designer handbags and clothing. The AFT's own audit also put Hemphill in the middle of years of misspending. Her attorney, Frederick D. Cooke Jr., has said Hemphill has been "as cooperative as we know how" with federal investigators.

Hemphill, born in Johnstown, Pa., moved to Washington with her husband, Lawrence Hemphill, in 1963 and soon got involved in politics by participating in a bus boycott organized by a civil rights activist named Marion Barry.

After working for the federal government, Hemphill became an assistant to Bill Lucy, the secretary-treasurer of the American Federation of State, County, and Municipal Employees. Along with her husband, a city employee, Hemphill grew close to the District's first mayor of the home rule era, Walter E. Washington, when Lucy chaired his campaign in 1974.

After a stint as an assistant in the Carter White House to political aide Timothy Kraft, Hemphill was a labor liaison during three of Barry's four terms as mayor. When Sharon Pratt Kelly became mayor in 1991, Hemphill shifted career tracks to manage the city government's security force, a job that required her to sometimes wear a uniform and carry a gun.

After retiring from the city, she joined the teachers union office in 1996 and was an early Williams supporter in 1998, when that union broke with most others in the city to back him for mayor. The move gave Williams (D), a political neophyte, credibility in his battle against better-known elected officials.

It was during Williams's years in office that Hemphill came to full prominence as a player in administration appointments, as a member of the mayor's kitchen cabinet of political advisers, as a member of the Finance Committee and executive director of the city's Democratic Party and as co-chairman of the mayor's reelection campaign. The other co-chairman, Max Berry, was a white Georgetown lawyer, and political wisdom favored balancing the team with an African American woman from Ward 4, heart of black Washington's political class.

Before the nominating petition trouble began in July, Hemphill effectively managed the day-to-day campaign and had limited check-writing authority, campaign officials say.

One of the few other regular fixtures in the mayor's campaign then was consultant Charles N. Duncan, a longtime Hemphill friend from the Carter White House whom she helped recruit to the campaign. They oversaw operations when the thousands of fraudulent and forged nominating petitions were produced and submitted, and Hemphill helped deliver them to the city election board. Both have said they knew nothing about the forgeries, though the mayor's advisers have questioned Hemphill's explanations in recent months.

Duncan backed her account in a recent interview, saying they were focused on other matters during the crucial campaign weeks. He also expressed doubt that she defrauded the union. "I'm going to reserve judgment," he said. "Someone who has worked as hard as she had doesn't deserve this."

Even after the petitions exploded into a humiliating scandal for the mayor, costing him $250,000 in fines and a spot on the party's primary ballot, Williams remained loyal and resisted calls from top advisers to remove Hemphill as campaign co-chairman, say those close to the campaign.

When the teachers union scandal broke in October, the mayor at first defended Hemphill, saying: "I stick by my friends. . . . She's worked very, very hard for me."

But the tone has changed as more allegations have come to light. "I have not, do not, run the teachers union," Williams said last week. "I have nothing to do with the problems that have afflicted the teachers union by individuals whose behavior was horrible."

Perhaps one measure of Hemphill's declining clout can be found in the change of fate of her husband, whose rise through city government had once roughly paralleled his wife's growing power.

Lawrence Hemphill started in 1972, working on community relations for the D.C. Department of Human Resources. He was a special assistant in the D.C. Department of Employment Services during Barry's mayoral era in the 1980s. Under Kelly in the 1990s, Hemphill helped manage housing programs. Finally, under Williams, he reached a Cabinet position, making $85,286 a year as the mayor's director of community outreach.

Williams briefly transferred him to the city's Transportation Department as the scandal heated up; Lawrence Hemphill's name appeared in a federal affidavit, allegedly for paying to have the $13,000 union-bought television installed.

The mayor recently announced Lawrence Hemphill's departure from city government, effective Friday, "by mutual agreement." But the Hemphills' son-in-law, Michael Martin, who faces allegations of helping to misspend union money, still has his job with the city Health Department.

Staff writers Justin Blum, Yolanda Woodlee and Neely Tucker and researcher Bobbye Pratt contributed to this report.

Gwendolyn M. Hemphill confers with attorney Frederick D. Cooke Jr., who says she is working with investigators.