James Roosevelt Jr. '68 challenged Joseph P. Kennedy II to a half-hour televised debate in their bids for the 8th Congressional District Democratic nomination in the Sept. 16 primary, but Kennedy aides said no.

At a news conference Wednesday outside Kennedy's campaign headquarters, Roosevelt said he had purchased time on WNEV-TV, Boston's Channel 7, for a one-on-one debate with the front-runner. Kennedy leads the polls, which give him about a third of voter support. Other voters appear to be split among the 10 remaining candidates. Melvin H. King and State Sen. George Bachrach are tied for second place, while other candidates lag behind.

Roosevelt's support ratings have never exceeded 10 percent, and have recently equaled those of State Rep. Thomas M. Gallagher (D-Allston), who withdrew from the race yesterday.

The candidate, who has tried to portray the race as a competition between his own famous name and Kennedy's, said he had committed $7,000 for time at 7:30 p.m. Saturday, July 26.

"I think I'd make a better congressman than Joe Kennedy and I'm confident I can prove it if the voters have the opportunity to evaluate us head to head," Roosevelt said.

Roosevelt recalled the vow Kennedy made in his January announcement speech to debate his opponents "one at a time, or all at once."

Kennedy spokesman Chuck McDermott accused Roosevelt of "practicing the politics of exclusion." He said Kennedy has "too much respect" for his other opponents "to exclude them from the dialogue. It's unfair to the voters."