Kathleen Kennedy Townsend, daughter of the late Sen. Robert F. Kennedy, officially announced her candidacy today for the 2nd District congressional seat in Maryland, currently held by Republican Rep. Helen Delich Bentley.

In an American Legion hall crowded with more than 400 supporters, including three generations of Kennedys, Townsend, 34, invoked the "patriotism, idealism, courage and honesty" of her father and her uncle, President Kennedy, whose birthday is celebrated today.

But the Democrat added, "I do not ask for support because of my family name," and vowed to run a grass-roots campaign of door-to-door canvassing and neighborhood coffee klatches.

Townsend, making her first bid for public office in a district that forms a northern horseshoe around Baltimore and includes Baltimore County and part of Harford County, described her race against Bentley as "an uphill fight." Bentley ousted 20-year Democratic veteran Clarence D. Long in 1984 after two unsuccessful races against him.

Townsend, her three young daughters playing on the stage beside her, delivered a 15-minute speech and promised to "take charge of our future" by attacking problems from the economic to the environmental. She cited the need to "stop the senseless spiral of nuclear weapons" and "build a strong defense" by fostering competition to produce cost-effective weapons.

"I was raised to believe that if each of us makes a ripple, we can together make waves that improve the lives of children and our communities," she said.

Townsend pledged to give priority to upgrading education by instituting a "teacher corps" that would finance college for prospective teachers in exchange for several years of work in public schools.

Bentley, a former Baltimore Sun reporter and Nixon administration official who has lived in the area for more than 30 years, has, along with some political observers, questioned whether Townsend can win in a district in which she has lived only briefly. Townsend moved to Towson with her children and husband David, a faculty member at St. John's College in Annapolis, just under two years ago.

But Townsend, a lawyer who recently quit her job in the state attorney general's office to campaign, said, "I have a real commitment to this area."

Townsend estimates that she will need between $500,000 and $1 million to wage the campaign. She has raised $220,000.

In reports filed with the Federal Election Commission this spring, Townsend reported $151,443 in contributions, much of it from relatives and supporters in Massachusetts and New York.

She is one of two in the most recent generation of Kennedys to emerge on the political scene. Her brother Joseph P. Kennedy II is running for the Massachusetts congressional seat being vacated by Democratic House Speaker Thomas P. "Tip" O'Neill Jr. Joseph Kennedy was in the audience today with scores of family members, including Robert F. Kennedy's widow Ethel and seven of their children.