Less than an hour before President Reagan took to the airwaves to announce his latest offense in the battle of the budget bulge, Maryland Democratic officialdom took to the podium to do a little pre-game quarterbacking of its own.

"The fight, ladies and gentleman, begins tonight. In about 45 minutes President Reagan is going to go on television and concede that he was wrong, that his budget will not work," said Montgomery County's U.S. Rep. Michael Barnes. "Tonight the president's speech will be the comeback of the Democratic party.

"Ladies and gentlemen, let's go get them!"

And go get them they did. While Reagan was in the Oval Office, warming up to ask for an additional $13 billion in spending cuts last week, speaker after speaker at the Democratic rally reached from the balloon-festooned platform for just the right stinging denouncement of Reaganomics.

From Gov. Harry Hughes to Sen. Paul Sarbanes to County Executive Charles Gilchrist, each had his own particular criticism to unleash before the gathering in the Bethesda-Chevy Chase High School gym.

A crowd of about 200 cheered and applauded each additional jab. The import of the rally, however, lay not so much in the attack on Reagan as in the message state party leaders were sending to the ranks: we're not afraid to embrace the much-maligned, so-called liberal Democratic policies. For this group, anyway, Franklin D. Roosevelt and New Deal policies were called from the bench to play the front line; Calvin Coolidge and fiscal conservativism were banished to the sidelines.

From Hughes: "Coincidentally, I have just spent the afternoon meeting with the president and 15 other governors. We've spent the last two to three months trying to cut the 20 to 25 percent from our state budget that he originally requested. And, now, he's turned around and asked us to cut another 12 percent from the same programs. It's hard to believe."

From Sarbanes: "What this administration doesn't realize is that a lot of expenditures demonstrate a wise investment in the future -- health care programs, job programs, immunization programs, black lung programs. Why cut here? Why don't they try to get back some of the $12 billion they gave to the oil companies in the latest budget?

"Franklin Roosevelt brought most Americans into the mainstream of American life. Ronald Reagan is trying to move America back toward a two-class society: a small group of the rich at the top, and then the rest of us. We're not going to let that happen. . . . David Stockman's budget is not going to be balanced on the backs of Social Security people."

From Gilchrist: "It's incredible that a person as irresponsible as the president could have ever been a public official. There are problems in the schools, so he shuts down the Department of Education and reduces school lunches . . . ."

And from county party chairman Stanton Gildenhorn: "The New Deal is not dead yet. . . . I will ask you the same questions Reagan asked in the October 1980 Carter-Reagan debate: Are you better off financially now than you were in November 1980? Can you buy a house? Can you buy a car? Indeed, can you get a job? If you can answer yes to those questions, then you can stick with those clowns in 1982. Tonight we say to the American electorate, 'All is forgiven. Welcome home.' "

Finally, Barnes, looking banker-dapper in a white shirt and navy blue tie, drew the biggest laugh of the evening. From his list of how Republicans differ from Democrats:

"Republicans are different from Democrats because they tend to sleep in single beds and in separate rooms. That, of course, is why there are more of us."