First Lady Nancy Reagan saluted Eleanor Roosevelt on the centennial of her birth yesterday, and if it looked to some Democrats as if the Republicans were trying to steal yet another of their heroes, it didn't look that way at all to Eleanor Roosevelt's family.

"It was a beautiful luncheon," said James Roosevelt, one of three Roosevelt sons at the luncheon -- and one of two who said he plans to vote for Ronald Reagan again next month.

On a campaign swing to Detroit, Walter Mondale, who earlier accused Republicans of "grave robbing" by invoking the tradition of Harry Truman, John Kennedy and Hubert Humphrey though they had opposed their policies when they were alive, took sharp issue with Mrs. Reagan's gesture.

"You don't honor Eleanor Roosevelt by cozying up to racists in South Africa and dictators in Latin America," Mondale said. "You honor her by standing up for human rights everywhere in the world."

Picketing outside the White House were Rep. Pat Schroeder (D-Colo.), Eleanor Smeal, former president of the National Organization for Women, and other feminist leaders who called Reagan administration policies on civil and women's rights "an affront" to Eleanor Roosevelt's memory.

Their remarks later drew an irate rebuttal from Maureen Reagan, one of her stepmother's luncheon guests. "Those people out there are never going to get into this house and that's why they're upset," she said.

She was equally critical of Mondale's remarks. "Presidents have a certain feeling for other presidents with whom they may have agreed or disagreed. Things upon which they agreed are the things that make this country continue to be strong, which is why Mr. Mondale will never be president," she said.

Accusing Mondale of "lying" about Social Security cuts in the presidential debate against her father, she called the outcome "a draw -- and I think we win in a draw . . . I think they both looked tired at the end. Mondale's makeup was beginning to drip."

In the crosshall of the White House, whose current occupant likes to tell how he used to vote for Franklin Delano Roosevelt, James and Elliott Roosevelt seemed unaware of the fracas.

It wouldn't shock his father in the least that two of his sons are voting again for a Republican president, said James Roosevelt. "He voted for Republicans himself," specifically Theodore Roosevelt and New York City Mayor Fiorello La Guardia. "There might have been others."

Elliott Roosevelt told of voting for Richard Nixon once "and I really got my comeuppance."

A third brother, Franklin Roosevelt Jr., however, said he will vote a straight Democratic ticket "from top to bottom. I've always been a Democrat and I believe Mondale is expressing in today's terms the same principles which I felt made our party the party of the majority."

He said he had not discussed his choice or political views "at all" with either of his brothers. "We respect each others' opinions," he said.

A Roosevelt grandchild, Chandler Roosevelt Lindsley of Dallas, Elliott Roosevelt's daughter, recalled some "very lively" arguments over political issues among the Roosevelt sons as they sat around the dinner table at Hyde Park.

"As a child I thought they were serious, of course. My grandmother just adored arguments. She sat at the end of the table with a grin on her face. Occasionally she would interject, and that would be the last word," said Lindsley, one of eight grandchildren at the luncheon.

Jonathan Lash, Eleanor Roosevelt's godson, who remembers sitting very quietly for long periods of time through some of those Hyde Park meals, recalled that one discussion resulted in a Roosevelt son knocking over a martini into a Christmas centerpiece.

"They've all mellowed so now," said Lindsley, looking over at Mrs. Reagan's table, where the brothers appeared to be on good terms and good behavior as they ate crab supreme and veal tenderloin.

Calling Eleanor Roosevelt "a truly great American lady" who always seemed to be "larger than life to me," Mrs. Reagan said in prepared remarks that "no person's problem was too small to attract her attention -- and today we can only guess at the scale of her generosity because so much of what she did was without fanfare and in secret."

Said James Roosevelt: "She dearly loved people. In fact, I think she knew more people because of my father's polio perhaps than he did himself. And therefore she was a wonderful reporter throughout his political career."

Earlier, the first lady said that while "I didn't agree with everything she did, you couldn't help but be a fan. Whether you were a Republican or a Democrat didn't make any difference. But I wasn't politically involved at that time -- politics never entered my mind until my husband, and now -- three more weeks, four more years."

Entertainment was an excerpt from an off-Broadway play about Eleanor Roosevelt, "First Lady."