Montgomery County Council member Michael L. Gudis, challenged by a Dickerson area civic group to withdraw his vote in favor of a controversial $170 million, energy-producing waste incinerator in that area because he owns stock in Potomac Electric Power Co., said yesterday that he stands by the waiver he was granted by the county's Ethics Commission allowing him to vote on the issue.

The Sugarloaf Citizens Association contended in a letter to the council member that he had violated the county's conflict-of-interest regulations by participating in the vote last month. The measure passed the council 4 to 3, and a withdrawal by Gudis would have had the effect of defeating the issue and forcing the council to vote again. Gudis owns 2,138 shares in the utility, which owns the land where the mass burn facility is to be built and will buy steam energy produced there.

Gudis said the county attorney's office had assured him that he was covered by a waiver of the conflict rules issued by the Ethics Commission in his behalf and for two other officials in December 1985. County Administrator Lewis T. Roberts owned 163 shares and environmental protection Manager Eric Mendelsohn owned 47 shares. Pepco stock split 2 for 1 in May and closed yesterday at $21.75 a share. Pepco has more than 94.4 million shares outstanding, a company spokeswoman said yesterday.

Lynn Lipp, president of the Sugarloaf civic group, said the incinerator, which her group opposes, was not one of the options being considered when Gudis was given his waiver, and that Gudis was given permission only to vote on one of four other options.

Gudis said he "took the trouble to ask for a waiver" because it was "a major decision affecting the entire population of Montgomery County. I felt that I was elected to represent the citizens of Montgomery County and to cast my vote."

The county code prohibits elected officials from having financial interests in firms that negotiate contracts with agencies on which the officials serve.

The citizens association suggested in its letter to Gudis that Pepco would benefit from the council decision, saying that the company's application to the state to double its plant size at Dickerson was "not independent" of the council action.

But Pepco spokeswoman Nancy Moses said the application to add capacity bore no relation to the trash incineration plans and, in any event, was filed a month before the council vote. The additional plant will burn oil, gas or coal, she said.

"There is no legal reason for Gudis to withdraw" his vote, said Assistant County Attorney Rocky Sorrell, who represents the Ethics Commission.

He said the request "appears to be a tactic by the citizens out there who are opposing this."

"When you're opposing something you use whatever means you have at your disposal to try to defeat this project," he said. "That's exactly what they're doing. I'm not criticizing them for it, but they're off target."