A summit conference today on the sewer war between Montgomery and Prince George's counties has been canceled because the Prince George's County Executive refused to attend.

County Executive Lawrence J. Hogan said yesterday he would boycott the scheduled meeting which was hoped to end the feud, because the Prince George's county council had rejected one of his appointments on Tuesday.

This act "of the Democratic machine" deprived him of the counsel he needed to participate in the sewer negotiations, said the Republican."If Hogan doesn't attend, there's no point," said a spokesman for Montgomery County Executive Charles W. Gilchrist. If Hogan isn't coming Gilchrist won't be there either, the spokesman said.

The two counties, which make up the Washington Suburban Sanitary Commission, have been fighting over which county gets to use what percentage of various sewage treatment plants that must treat wastes from any new buildings in either county.

Each county has three members on the WSSC appointed by the respective county executives. And each county executive wants to insure that his representatives on the bicounty agency fight on the "right" side of sewer war.

On Tuesday, both county executives tried to change their representatives on the commission. Hogan's proposed representative was voted down 10-1 by his county council, and Gilchrist announced his intention to remove Bert Cumby, one of Montgomery's WSSC commissioners.

Yesterday, the three Prince George's commissioners united to elect Cumby chairman.