Montgomery County Council President Rose Crenca, reigniting debate over the location of an expensive new trash incinerator, released new figures yesterday that showed that building the facility at Dickerson would cost twice as much as placing it at Shady Grove.

The council, on a 4-to-2 nonbinding vote last week, tentatively decided to go along with County Executive Sidney Kramer's request to place the $170 million facility in rural Dickerson at the western border of the county. But the tenuous alliance of council members who favor the Dickerson site appeared to be in jeopardy yesterday, with at least one council member reevaluating his position.

Isiah Leggett, who voted with the majority, said he is "looking at everything" in preparation for Tuesday's formal vote.

The incinerator has become one of the most controversial issues of Kramer's first year in office, with the council wavering in the past few weeks over which site to choose. At stake in the council decision is the county's long-term plan for coping with growing amounts of garbage, as well as the immediate political fortunes of several council members.

Citizen groups on the two sides have targeted two council members as possible swing votes: Leggett, who is admittedly concerned about his credibility because he opposed the Shady Grove site during last year's election campaign, and Michael L. Subin, whose district includes the two sites and who voted for Dickerson.

Crenca noted that only one council member needs to switch sides in order for Shady Grove to be picked, although the council would then have to hold hearings on the site. Also favoring Shady Grove are council members William E. Hanna Jr. and Neal Potter, who has been absent from the council since having had heart attack in May but who may return for Tuesday's vote.

Crenca said she called a news conference because she wanted to make new information available to the council and to the public, including cost estimates prepared by council environmental analyst Stewart McKenzie.

According to the estimates, which McKenzie said he calculated with members of the executive's environmental protection department, the total cost to the county of a mass burn facility at Shady Grove would be $16 million to $18 million a year, compared with an estimated $34 million to $35 million a year at Dickerson. The cost to the typical household, which absorbs all costs of trash disposal, would be $34 to $38 per year with a Shady Grove facility and $64 to $70 per year with a Dickerson facility.

Council members were already aware that Dickerson would cost more than Shady Grove because garbage would have to be hauled there by rail and ash would have to be hauled back. But previous estimates had placed the extra cost at $10 million per year, or $24 per household.

McKenzie explained that the new numbers take into account the possibility of producing -- in addition to electricity -- steam that would be sold to heat and cool nearby buildings. He said this technology, called cogeneration, could be accomplished at Shady Grove, where there is nearby development, but not at Dickerson. One reason Dickerson had emerged as a favorite for the politically unpopular garbage facility is that only 10,000 people live in the area, compared with the estimated 200,000 people in the Shady Grove area.

The emotion of the issue was evident as residents of Shady Grove and Dickerson crowded into the press room at the council office building.

Kramer said later that his administration has not had time to study the numbers but that it is not news that Dickerson is the more expensive option.

Crenca disclosed that a meeting between the council and an official with the Northeast Maryland Waste Disposal Authority, under consideration to build and operate the mass burner, was canceled after objections from Kramer.

She said that Richard Gagliardo, an official with the authority, was going to present technical reasons for choosing Shady Grove.

Gagliardo said in a telephone interview that he told Crenca that he and Kramer had "an understanding" that it would be inappropriate for him to address the full council in a public session. Kramer labeled that "ridiculous" and said his only concern was that the council not delay a decision.