Convicted Rep. Charles Diggs (D-Mich.), who has said he would give up his chairmanship of the House District of Columbia Committee, may be forced also to give up a subcommittee chairmanship he wants to keep, when the House Democratic Caucus meets next week.

Rep. Matthew McHugh (D-N.Y.) will try to change the caucus rules to require the caucus to vote on any subcommittee chairman who has been convicted of a crime or censured, reprimanded or otherwise admonished by the House. Sources gave McHugh's proposal "a good chance" of passing.

At present the Democratic caucus votes only on full committee chairmen and subcommittee chairmen of the Appropriations committee. All other subcommittee chairmen are selected by the individual committees.

Diggs has argued that he should be allowed to keep the chairmanship of the African subcommittee on the House International Relations Committee because his chairmanship of that subcommittee was not involved in the crime for which he was convicted.

Diggs was sentenced to three years for taking salary kickbacks from his staff.

But McHugh and other Democrats feel a convicted congressman, or one who violated House ethics, should hold no position of power. In a letter supporting McHugh's proposal, Common Cause argued the full caucus has the responsibility of deciding what to do about members found guilty of misconduct and it shouldn't be left to the individual committees.

The proposed change would also affect Rep. Charles Wilson (D-Calif.), who was reprimanded by the House for taking money from Korean businessman Tongun Park in the Korean influence-buying scandals.

Wilson heads a Post Office and Civil Service subcommittee on postal personnel and modernization.

One other returning member of the House, Rep. Dan Flood (D-Pa.) has been indicted on bribery charges. Rep. Richard Ottinger (D-N.Y.) said a proposal also may be offered in the caucus to force indicted members to step aside as committee or subcommittee chairmen. This proposal is more controversial because of the principle that everyone is considered innocent until proven guilty in a court of law or by an investigation by the ethics committee.

Flood, who is chairman of the powerful Labor-HEW subcommittee on Appropriations, will have to stand for re-election by the full caucus to the subcommittee chairmanship. He is expected to be defeated or to withdraw before the elections, held in January.