The state Democratic Party's endorsement of Rep. James M. Shannon (D-Lawrence) for the Senate this month in Worcester appears more likely to confuse the race for retiring Sen, Paul E. Tsongas's (D-Mass.) seat than it is to clarify matters.

Although the 32-year-old Shannon beat Lt. Gov. John F. Kerry by 53.2 to 46.7 percent on the fourth ballot of the party convention June 9, Kerry, by most accounts, is still the narrow favorite to win the Democratic nomination in the mid-September primary.

Either Kerry, Shannon, former Speaker of the Massachusetts House David M. Bartley, or Secretary of State Michael J. Connolly will face the winner of the Republican primary battle between former Defense Secretary and Attorney General Elliot L. Richardson '41 and Walpole businessman Raymond Shamie.

Though no polls have been released in the two weeks since the convention, Kerry is expected to remain in front because he has high name recognition. He ran a successful statewide race for lieutenant governor in 1982--even after losing the party's endorsement--and he is positively identified with the popular administration of Gov. Michael S. Dukakis, an officially neutral observer in this race.

Kerry also stands to benefit from the active support of a number of local bigwigs, especially in the southeastern part of the state.

All of this begs the question: Why didn't he win?

Thomos R. Kiley, a Boston-based political consultant and chief of posting operations for the Kerry campaign, claims that Kerry did not expect to win the party endorsement, even though Kerry operatives invested heavily in Worcester and had what by all accounts was the best-run operation on the convention floor.

Kiley said that Shannon--who, for better or worse, has been labeled "Mr. Inside"--held all the cards at the convention, and had "the political leverage to work the inside game."

"We did put a lot of money into the convention, and that's the only reason we got as close as we did," Kiley added, "It was well worth the effort even in a narrow defeat."

Nonetheless, Kerry backers are terming the convention a "non-event" that was, and deserved to be, overshadowed by the Celtics 7th-game victory over the Los Angeles Lakers in the NBA Championships.

Kerry stands to benefit it this summer if the Senate race becomes a low-profile affair, hidden by the media glare of the Olympics, the Democratic and Republican National Conventions, and even Michael Jackson.

Come September, Kerry would win the four-man race on name recognition alone.

"Jim Shannon has the talent to do some damage but he has a roadblock in terms of media noise, the Olympics and the conventions," said political consultant Michael Goldman. "It'll be much harder to break through."

The convention victory has given three-term representative Shannon--until now little known outside his fifth district in Middlesex County--valuable statewide exposure, but it is now up to him to capitalize on the opportunity.

Shannon stands to benefit if Connolly--who barely made the 15 percent cut at the convention to stay in the race--fades away, as he is likely to do.