Warming up for his presidential race, former Democratic senator Paul Tsongas warned yesterday that Republican policies are mortgaging the future of the country and that traditional Democratic responses have outlived their usefulness.

Tsongas's appearance at the National Press Club was the latest stop in a hastily run circuit that has taken him in a matter of months from prospective candidate to certain entrant in the long-dormant Democratic presidential sweepstakes. He said he would formally announce his candidacy April 30 in his native Lowell, Mass.

"The odds don't bother me," Tsongas told his audience yesterday. "I was written off the four times I ran against incumbents." In each case, he added, his victory was described as a fluke. "This is going to be the fifth fluke," he predicted.

There are not many politicians who would agree with that prediction, but in a Democratic contest that so far has no other announced candidates, and only Virginia Gov. L. Douglas Wilder and 1972 losing candidate George McGovern taking overt steps toward entering, the self-confident Tsongas believes his chances are not as bad as others believe.

When Chrysler Corp. was battling back a decade ago, Chairman Lee Iacoccoa got famous appearing in television ads that said, if you can find a better car, buy it. Tsongas, a central figure in the legislative battle over the Chrysler bailout in 1979, offered a similar challenge to prospective Democratic opponents.

Clutching a copy of his newly printed, 85-page manifesto, "A Call to Economic Arms," Tsongas said, "This is my campaign -- the ideas, the vision, the direction . . . . If somebody has a better vision, write it, put it down, put it on the table, let's have a debate, and I will compare this to the administration's record."

Tsongas is not the first Democrat to use a white paper as a springboard to the presidency. Gary Hart tried in 1984 with a newly published book, and when he undertook his ill-fated comeback after dropping out of the 1988 campaign, he tirelessly promoted a 96-page booklet of speech excerpts and taunted opponents to do better.

Tsongas, who served two terms in the House and retired from the Senate after one term to battle cancer, criticized President Bush and the policies of his and former president Ronald Reagan's administrations as "generationally immoral" for piling up debt, allowing the U.S. trade balance to fall into near-permanent deficit and engaging in "happy talk" that he said avoids the problem.

"The president's vulnerability is his refusal to use his incredible popularity to do what's right for this country on domestic issues," Tsongas said.

But he spent as much time yesterday rattling Democratic cages, decrying creeping Democratic protectionism and political strategies of "class warfare and corporate bashing."

"In 1992, we're going to be a pro-business Democratic Party," he said, adding that he favored a capital gains tax cut. "For Democrats to view the business community as the enemy is so foolish."

Tsongas said he hoped to use his candidacy to become an "economic Paul Revere," sounding the alarm about America's decline in an effort to rally people to compete more effectively against Japan and Germany.

"When you read . . . about Sony buying up part of the American media, how did you feel?" he asked. "Did it not affect your national pride? That's what is at stake . . . . I want America to gain control of its economic destiny."

In a sign of Democratic skittishness about the impact of the Persian Gulf War on Bush's reelection prospects, Tsongas never mentioned the crisis during his prepared speech.

In response to a question, he conceded he would have voted against the resolution authorizing Bush to go to war.

"It seems to me I have to start off this campaign speaking the truth," he said.

He had little to say about defense or foreign policy issues, other than those dealing with economics. "I really believe that my major foreign policy advantage -- and you may well disagree with his -- is that I lived for two years in an Ethiopian village, and that I think I know how Third World people think, how they view us, how they make decisions."

To counter possible questions about his health, Tsongas brought along his physician, Tak Takvorian of the Dana-Farber Cancer Institute in Boston, who said his patient has been free of the lymphoma for five years and is in superb health.

"He's always been underestimated," said Thomas Kiley, a Democratic pollster from Boston. "That doesn't mean he's going to be president, but he has a fierce, dogged quality that serves him well."