Don’t tell US Congressman Barney Frank, a long-time Democrat from Newton, that the Democratic and Republican Parties look the same nowadays. Not only does he reject such an assertion, but he resents it. That, at least, seemed to be the general message at a Community Church of Boston forum Tuesday night.

To debate the future for progressives in this country — particularly after a devastating Election Day 2002, during which Republicans took over Washington, DC — the Community Church invited Frank to address a packed crowd of left-leaning residents and activists. What emerged is the veteran pol’s own challenge to city liberals: don’t give up on the Democratic Party yet, even if you’re disillusioned by its lurch toward the center of the political spectrum over the past decade.

" It’s the Democratic Party, alas, " Frank said with a smile, adding that " in every way " the Democrats surpass the Republicans on crucial policy matters. Frank, an openly gay politician, then ticked off the significant disparities between the parties: gay-and-lesbian rights, abortion, the environment, free trade. " Even economics, " he said. When Bill Clinton became president in 1993, for instance, his very first achievement was to pass an income-tax package that not only lowered taxes for middle- and low-income people, but also raised the tax rate on those earning more than $200,000. By contrast, George W. Bush’s first act upon moving into the White House in 2000 was to reverse his predecessor’s policy and lower taxes for those in upper tax brackets.

Progressives, Frank argued, can now follow one of two role models to push for more liberal politics — Jesse Jackson or Ralph Nader. Both men ran for president (Jackson in 1984 and 1988, and Nader in 2000) to trumpet a liberal agenda. Jackson, however, did so by running within the Democratic Party. As a result, he forced the Democrats to move further left. Nader, as we all know, became the Green Party presidential candidate and, said Frank, " had no lasting effect other than to help the Republicans win. "

Frank spoke for about 30 minutes, free-association style. He expressed his outrage over the Bush administration’s " abusive " policy of locking up illegal immigrants, particularly Arabs, without charging them with any crimes. ( " That’s extraordinary, " the congressman said.) And he discussed the topic foremost in people’s minds — the imminent attack against Iraq — bluntly ( " I don’t see how the Bush administration can continue to argue that Iraq is any kind of threat to us " ). To Frank, the looming US-Iraq war seems a perfect place for disgruntled progressives to begin to make a difference. He challenged those who oppose the war to write to Democratic presidential hopefuls — in particular, Massachusetts senator John Kerry — and urge them to oppose a US war against Iraq. " If people wrote, called, e-mailed, and faxed the Democrats, " Frank observed, " if they said, ‘This is a defining issue and I urge you to come out against it,’ the Democrats might help to persuade Bush not to do it. "

In closing, the congressman left the audience with one thought: " Remember, the best way to move the Democrats is the Jesse Jackson model. Push from within. " In other words, don’t be a Nader-style spoiler.