A broad coalition of District of Columbia Democrats announced yesterday the formation of the D.C. Committee for a Democratic Alternative -- in effect a committee supporting the unannounced candidacy of Sen. Edward M. Kennedy (D-Mass.) for president.

It is the second pro-Kennedy group established in the District. In July, community activist Norman C. Neverson and political fund raiser Mark Plotkin announced formation of the D.C. Kenndy for President Committee.

The Committee for a Democratic Alternative includes 17 members of the 64-member D.C. Democratic State Committee. The new Kennedy group is headed by Ward 3 Democratic Club Chairman Mary Ann Keefe and Ward 4 Democratic Club Chairman Barry Campbell.

C. Grove Smith, a spokesman for the group said that members of the organization opposed President Carter because they feel he can not win the 1980 election if nominated. Also his administration has made what they consider inadequate efforts to secure passage of a constitutional amendment giving the city full voting representation in Congress, he said.

"Most of the committee probably is pro-Kennedy," Smith said."But we have made a special point to include all those who believe Democrats can come up with a better candidate than Jimmy Carter."

Plotkin, head of the Kennedy committee, also expressed dissatisfaction with Carter's policies. "Senator Kennedy recognizes that urban concerns come first," he said.

Neither of the two committees contains any principal elected city officials. That can partially be explained, observers said, by the fact that the District of Columbia is dependent on the White House and the Carter administration for financial support.