Kathleen Kennedy Townsend, the oldest daughter of the late senator Robert F. Kennedy, said yesterday that she has quit her job so she can prepare for a potential challenge for the congressional seat held by Rep. Helen D. Bentley (R-Md.).

Townsend, 34, who stressed that she has not yet made a final decision on the race, would be the second of Robert Kennedy's children to run for Congress next year. Joseph P. Kennedy II, Townsend's younger brother, recently announced he was running for the Cambridge, Mass., seat of retiring Democratic House Speaker Thomas P. O'Neill Jr.

"I'm really planning to run, although I haven't taken the final steps. I haven't formed a committee. I haven't formally announced," said Townsend. She added that until she takes those formal steps, there is the possibility that she will not run. Townsend, a Democrat, said that she left her job in the Maryland attorney general's office on Friday, in preparation for the race for Maryland's 2nd District congressional seat. She said she has talked to numerous elected officials and others in recent weeks, trying to gather support for her candidacy. She added that the response has been very favorable and that she expects to make a decision in the next several months.

Townsend estimated she would need between $500,000 and $1 million to run for the Baltimore County seat, which Bentley has held since 1984 when she defeated 11-term Rep. Clarence D. Long (D-Md.) after two unsuccessful bids.

Earlier this year, Democratic Party officials said they thought they had a good chance of unseating the tough-talking Bentley, who as a freshman was considered vulnerable. But their predictions were based on the assumption that Democratic Baltimore County Executive Donald P. Hutchinson would challenge Bentley. Hutchinson's decision to run for the U.S. Senate left Democrats searching for a candidate to face Bentley.

Townsend's name has been mentioned in recent weeks by Democrats who say her family name would be a plus in getting publicity and funds. Townsend, who is a lawyer, and her family moved to Towson from Boston about 1 1/2 years ago, when her husband, David, took a teaching job at St. John's College in Annapolis. She worked for four months in the attorney general's office, specializing in environmental issues. Townsend said she and her family wanted to live in Maryland, because her husband grew up there and because his parents still live there.

In addition to trying to gauge support, Townsend said she is trying to decide whether there are important issues she wants to campaign on. "I don't want to run unless I have something to say," she said.