Stepping up the Clinton Administration's campaign against gun violence, Hillary Rodham Clinton used an emotional White House ceremony today to call on Americans to press Congress to ''buck the gun lobby'' and pass several gun control measures.

Today's event, pegged to Mother's Day, which is Sunday, was held in the formal East Room of the White House and featured three parents of children killed or wounded by gunfire. They included Tom Mauser, whose son Daniel was killed last month in the shooting rampage in Littleton, Colo. His story of waiting for word about his son's fate brought Mrs. Clinton nearly to tears as she took the podium and gravely addressed an audience of other parents who had lost their children in shootings.

The Senate is to begin debate next week on a number of gun control measures, some of which mirror proposals offered recently by President Clinton. ''The senators need to hear from all of us,'' Mrs. Clinton said. She urged voters ''to give them the encouragement to do what they know is right and to remind them that there are many, many millions of American voters and citizens who will stand behind political leaders who are brave enough to buck the gun lobby, wherever that may take us, so that they will vote for the measures that we know will save lives.''

Mrs. Clinton was as careful as her husband has been to say that there are many causes of violence and that parents need to take responsibility for their children's behavior. But Mrs. Clinton, who is considering running for the Senate from New York, where gun control is popular, has also been more forceful than the President in directly taking on the powerful gun lobby in the aftermath of the Littleton killings.