At dueling press conferences in Rockville yesterday, members of the Progress Club portrayed themselves as good old boys whose club activities center on charity, while the Montgomery County state's attorney and Rockville's police chief countered with allegations that the club was an illegal gambling business where more than $25 million was at risk in poker games during a 28-month period.

The public salvos were fired just one week before Progress Club Inc., the corporation that runs the 500-member club, goes on trial before a jury in Montgomery Circuit Court on charges of operating a place for gambling.

Twenty-one club members were arrested on charges of illegal gambling June 5 by Rockville police after a 5 1/2-month investigation of the club. Charges of illegal gambling against all but one of the men were dropped after they performed community service.

Wearing black and blue buttons proclaiming a "Raw Deal in Rockville," Progress Club members feted reporters yesterday morning with bagels and cream cheese at 10:30, and a lunch of cold cuts and salad an hour later. In between the buffets, club officials decried the police department's and prosecutors' efforts. Club officials do not deny that members gambled, but they contend it was limited to harmless card games.

"The only thing these men could possibly be guilty of is being too doting a grandparent," said Herman E. Eig, 73, and a club member for 43 years. Eig, a retired businessman and real estate developer, added that two-thirds of the club's members are over 60.

But at a more somber press conference three hours later, Rockville Police Chief Jared Stout said his department's investigation showed that between Jan. 1, 1982, and April 1 of this year, 25,480 poker players had risked $25.4 million in card games. They also said the median age of members was 45.

Added State's Attorney Andrew L. Sonner: "This kind of operation would not be legal in any jurisdiction in the United States, including Las Vegas . . . . This was a business for the operation of a gambling casino, not a friendly little card game in somebody's home."

Sonner said he and Stout were "reluctant" to call the unusual conference close to a trial, but said it was necessary to counter inaccuracies from the club's media blitz.

According to Sonner and Stout, state police in Maryland and Florida, and New Jersey's special organized crime unit are jointly investigating three club members for possible links to organized crime. In addition, Sonner said, the "historical" link between organized crime and gambling had led officials to enforce antigambling laws.

At the morning press conference, Stanley Karlin, the club's president-elect, rebutted allegations about the club that he attributed to police and prosecutors. He challenged them to prove allegations that the club runs "the largest casino-type operation in the state," and "has links to organized crime."

Karlin said discussions are under way between club officials and state legislators to seek an amendment to Maryland gambling laws that would allow high-stakes card games at social clubs such as the Progress Club, an amendment that Sonner said he would not oppose.

Eig said that out of total club revenues of $458,000 in 1983, $235,000 came from sales of cards and fees for poker and gin rummy games. The club officials said they could not say how much money was at risk during the games.

Prepared statements at the club's press conference focused on the $35,000 to $40,000 donated by it annually to area charities. But Stout said that amount paled when contrasted with the $25.4 million club poker players risked during the 28 months investigated by police.

"The fact that one donates to charity does not remove other obligations to obey criminal law," Stout said.

"I have never heard a more . . . ridiculous figure in my life," Eig said of the $25 million amount.