WASHINGTON, Sept. 16— When Mary L. Landrieu first showed up for work at the Louisiana Statehouse after being elected to the Legislature right out of college, some male colleagues whistled at her, mocked her from the microphone and put a rubber snake in her desk. For a time, she regularly cried in public.

This year, as a United States Senator, she has had another dubious debut. Republicans began a full-scale investigation last spring into possible voter fraud in the close election that sent her to Washington in January. But this time, an hour after the inquiry was announced, she went in-line skating with her 5-year-old son.

And this summer, with Democrats threatening to stall work in the Senate unless Republicans called off that investigation, she adopted a baby and worked with an architect on the house she and her husband are building four blocks from the Capitol.

Ms. Landrieu, 41, was seated conditionally, while her opponent, State Representative Louis (Woody) Jenkins, pressed accusations that he was robbed of the election.

She still gets tearful sometimes, as she did in a recent interview when she talked about her mother, Verna Landrieu, and her father, Moon Landrieu, the former Mayor of New Orleans, seeing her sworn in ''under a cloud.'' But she's had a rather operatic career that has toughened her, and colleagues have been surprised by her resilience during the inquiry.

Ms. Landrieu has maintained that her campaign did nothing to taint the election, and the inquiry has so far turned up nothing significant, said Senator John Warner, the Virginia Republican who heads the Rules Committee. Democrats stalled committee meetings on five days but then called off the slowdown pending a hearing on Thursday at which the Rules Committee will hear testimony about whether gambling interests supporting Ms. Landrieu influenced the election.

But Mr. Warner seems to have lost his taste for the case, a cause celebre for conservatives.

''My guys want blood -- well, not my guys -- but I don't care any more,'' Mr. Warner said in an interview last week. ''I've seen it all and I just want to do my job.'' He expressed annoyance at finding himself damned by both the left and the right and distanced himself from Mr. Jenkins by saying: ''My client is the Senate. It's not Woody Jenkins.''

He did not, however, say the inquiry was over.

Meanwhile, Ms. Landrieu is keeping busy. ''To our somewhat utter astonishment, she is handling her senatorial duties in a remarkable way and is busy building a family while under as much pressure as a woman can possible endure,'' Mr. Warner said, ''and every day with a smile on her face and a stride that says, 'I can do it.' ''

On a recent day, she was up at 3 A.M. with her 10-week-old baby, Mary Shannon Snellings; at 8 A.M. she was out the door of her temporary residence, a Capitol Hill apartment, in a TV-friendly turquoise suit. She stopped at a kindergarten to drop off her son Connor, who used the drive time to extract a promise that she would ice skate with him this winter. (''You know what you need to do, Mom?'' he asked. ''You need to wear a booty pillow.'' She replied, ''O.K., Connor, I'll wear a helmet and a booty pillow.'')

On the way to work, she and her husband, Frank Snellings, a lawyer, passed the lot where they're planning to break ground this fall, a former parking area for a doctor's office. Nearby, they pointed out, are their drug store, their dry cleaner and their pediatrician's office. But for all their efforts to move here permanently, they were silent for a long moment when asked how they like Washington.

''It's not a friendly place like Louisiana,'' Ms. Landrieu said finally.

But there are lots of visitors from home and the day included breakfast with constituents. Ms. Landrieu is a hugger, a winker and an absolutely indiscriminate arm-patter, and she charmed the small crowd. ''I figured you'd get up here sooner or later, the best and the brightest,'' she told a visitor from Baton Rouge, while administering a series of arm pats. Still, her guests' eyes glazed over as she talked with great enthusiasm about a program for children she recently visited in Israel.

Children are a major focus for Ms. Landrieu, and her first piece of legislation, adopted as part of an appropriations bill two weeks ago, provides $5 million in block grants for adoption services.

In a series of morning meetings with more constituents, she also showed a fluency in the vocabulary of Louisiana issues, like imported crawfish and offshore drilling.

Family and friends said she is an idealist with big ideas and takes in strays -- animals and people.

She also has great confidence in her own moral compass, though her good deeds have not always been appreciated at home. She once lent out not only her own clothes, but her sister's as well, and as an adult, once picked up a homeless puppy and then dropped him off at her brother's house. She is not a woman who wonders about her place in the universe.

She grew up in politics, of course, in a family an aide calls ''the Kennedy's of Louisiana.'' And as the oldest of nine children -- after Mary comes Mark, Melanie, Michelle, Mitchell, Madeleine, Melinda, Martin and Maurice -- and she always seemed to be in charge.

''At the earliest ages she showed a remarkable herding ability, like a sheep dog,'' said her father. She once threatened to beat up some boys in the schoolyard if they did not stop picking on her brother, Mark. (They stopped.) And her family still laughs about the time when she was about 7 years old and her parents had gone out for the evening. When they returned, they found a note on their bed reporting that ''Mark was very bad tonight and Melanie was fine.''

''It was a report from Miss Boss,'' said her sister, Melinda Seiter. ''She had to come to the call and help a lot and she always thought she had to be the one to save everybody and everything.''

At the Ursuline Academy in New Orleans, she was president of the student council, and as she put it, ''practically co-principal'' with the nun in charge, Sister Anthony. ''I did pretty much run the school,'' she said, adding that she learned to be strong from the nuns.

That does not mean she is altogether calm about her situation. After narrowly missing riding in a Capitol elevator with Mr. Warner on the way to a vote, she went to the Democratic Party headquarters to make fund-raising calls to defray the $500,000 she has spent on lawyers so far to defend her seat. As she does three times a week there, she dialed for donations. And while she waited to take return calls from potential donors, she blasted the Senate and the Republican leadership.

''Not only do you run and win your race, now you have to spend the first year defending your race. They've moved the goal posts! And what's to prevent them from keeping me under this cloud for 4 or 5 years?''

When she talked about her parents' coming to see her sworn in, her eyes filled with tears. ''They were so proud to sit in the U.S. Senate and yet to see on that first day read into the record that it was a contested election -- my mother is a strong woman but it was almost more than she and my father could take.''

A few minutes later, though, on her way back to the Capitol, she was in high spirits again with her chief of staff, Norma Jane Sabiston, a friend since the two were in high school. After the Senator grabbed her friend's purse and fished out some makeup, Ms. Sabiston said, ''I need to give you that lipstick; it looks better on you.''

''Most things do,'' the Senator retorted, and they laughed as if they were on their way to gym class.

While serving under these circumstances is tough, Ms. Landrieu said, it has not been as hard as her early days as a state lawmaker.

After eight years there, she was elected state treasurer. In 1995, she lost a race for governor after a black opponent, former Representative Cleo Fields, accused her of running a racist campaign by suggesting that blacks should vote for her because she was the only Democrat who could win. She called the charges nonsense, and said they were also hurtful because her father is well-known as a civil rights advocate who opened New Orleans government to members of minorities.

After that loss, she jumped almost immediately into the Senate campaign. Then a week before the election, she was broadsided by an old family friend, the popular, retired Archbishop Philip Hannan of New Orleans, who called a news conference to announce that voting for her would be a sin because she supports abortion rights. She said she dropped 25 percentage points in the polls overnight in one area. She eked out a victory by just 5,788 votes only, to face Mr. Jenkins's challenge.

''She hasn't had this fairy-tale meteoric rise,'' said her lawyer and friend, Tony Gelderman. ''She has struggled every step of the way.''

But, he said, ''I've spent many years watching people that attack her end up vanquishing themselves. And she always dusts herself off.''

Photo: Senator Mary L. Landrieu, Democrat of Lousiana, with her 10-week-old daughter, Mary Shannon Snellings, has not let an inquiry into election fraud accusations keep her from building a life in Washington. (Amy Thompson for The New York Times)