As unemployment jumped again, the Democrats yesterday blasted the Reagan administration economic policies with their loudest salvo of rhetoric since they lost the White House.

The theme of their comments was that the recession that kicked the jobless rate up to 8.4 percent last month was no accident but was the "deliberate" result of President Reagan's tax, budget and monetary policies.

California Gov. Edmund G. (Jerry) Brown Jr. (D) told a Capitol Hill news conference that "the policy of high interest rates and deliberate recession" has produced a "free fall" recession that will cause record federal deficits and severe cutbacks in state revenues as well.

Sen. Daniel Patrick Moynihan (D-N.Y.) said that the recession "didn't just happen. It was made to happen." Moynihan told an eastern regional conference of the Democratic National Committee that Reagan's policy was "at war with itself," in combining deep tax cuts with high interest rates. "And when you're at war with yourself," he said, "all the casualties are your own."

Sen. Edward M. Kennedy (D-Mass.) said in a lunch address to the DNC conference that although there were 9 million unemployed, the highest number since 1939, "you can't accuse this administration of incompetence. They deliberately set out last January to create a relentless Republican recession--and they did it in record time." At a DNC dinner meeting at the Washington Hilton, Kennedy's colleague, Sen. Paul E. Tsongas (D-Mass.), argued that "the Republicans are in trouble . . . because Ronald Reagan took the applause lines from the campaign and made national policy out of them. Conservative simplicities are on a collision course with reality."

But Tsongas struck a somewhat more cautionary note when he said that "as Reaganism unravels in 1982, Democrats may run into a trap if we rush ahead" without carefully considering their own policies.

Saying he was "very concerned that the smell of easy victory may cut short the needed debate within our party," Tsongas said, "As Ronald Reagan twists slowly, Democrats cannot turn to relaxation or rhetoric. Our job is to keep . . . developing alternative policies that will work."

Most Democrats were content yesterday just to point the finger of scorn at what they said were the failed promises of Reagan's economic revolution. "The great economic irony of our time," Kennedy said, "is that Ronald Reagan, who reached the White House on a solemn promise to balance the federal budget, will be remembered as the president who brought the United States the largest budget deficit in our history."

Next week, the coordinated set of House committee field hearings on the effects of Reagan's policies will go into an accelerated schedule.

On Monday, full or partial units of four House committees and the Democratic caucus will hold hearings in Philadelphia, Pittsburgh, Cleveland, Providence and Indianapolis.

The Ways and Means Committee, which will be in Indianapolis on Monday, will move to hard-hit Detroit on Tuesday for what House Democratic leadership aides hope will be the most dramatic depiction yet of the recession's impact. Scheduled witnesses include top city and state officials, United Auto Workers leaders and members and representatives of public and private social welfare agencies.

Republicans, who boycotted an earlier Ways and Means Committee hearing in Baltimore, have changed tactics and will send at least one member to represent their party at the Indianapolis and Detroit hearings.

Rep. Guy Vander Jagt (R-Mich.), a Ways and Means Committee member and chairman of the Republican Congressional Campaign Committee, said that Republicans still regarded the field hearings "as a partisan show," but said that "there was so much obviously erroneous testimony at the last one that we thought having someone there might lend a little more accuracy to the record."