Two of the Democratic Party's best stump speakers joined voices here today as Geraldine A. Ferraro and Jesse L. Jackson teamed up to club the Republicans on issues ranging from civil rights to President Reagan's leadership.

"We must measure an administration by its character, not by its personality," Jackson told a wildly cheering crowd of 3,000, evenly divided between blacks and whites, at Memphis State University. Hundreds more were turned away at the door by the fire marshal.

"We are told by Jesus himself that you judge a tree not by the bark it wears but by the fruit it bears . . . . There's a character deficit in the Reagan administration."

In his pound-the-pulpit style, Jackson also registered dozens of new voters while leading them in a chant of "Give peace a chance, give Reagan the ranch." He accused Reagan of being "a reverse Robin Hood, taking from the poor and giving to the rich. That's not fair."

"In Lebanon, they ignored intelligence reports" before the U.S. Embassy annex was bombed Sept. 20, he continued. "In South Africa, when blacks were shot down, they ignored it. In Central America, they mined the harbors . . . . That's not fair."

Ferraro, in her first campaign appearance with Jackson, was overshadowed by the power of his rhetoric but picked up on the theme. "If you're homeless, they say you like it that way. If you're without a job, they say vote with your feet," she said. "And if you're hungry, they say eat cheese."

The Democratic vice-presidential nominee also blamed Reagan for the Senate's failure this week to pass a civil rights bill, saying, "Ronald Reagan has dragged his feet on every piece of civil rights legislation that's come before him."

Earlier in the day, Ferraro drew more than 10,000 supporters to a noisy outdoor rally in downtown Atlanta, where she again excoriated Reagan's response to the bombing of the U.S. Embassy in Beirut.

"At last, Mr. Reagan says he's responsible. Okay, tell me what that means . . . . When President Reagan takes responsibility for the embassy bombing, does he mean he didn't heed the many warnings that preceded the attack?" she asked.

"When the hostages were held in Iran, all through that 14-month ordeal, President Carter never once blamed someone else, and I for one was proud of my president . . . . This president Reagan let us down, and this president should pay a price," she said.

The crowd in Atlanta was unusally colorful and responsive, roaring answers to Ferraro's rhetorical questions. They included one true believer who hollered, "Uh-uh, we can't," after Ferraro demanded, "Name the last time Ronald Reagan took a chance for social change."

Among the placards aloft: "Punks for Gerry" and "Whatever My Mom Likes I like the Other -- Go Ferraro." There were also a few naysayers. One sign protested, "It's Not Carter-Mondale, it's worse. It's Mondale-Ferraro.