A presidential aide confirmed yesterday that he invited palimony lawyer Marvin Mitchelson to the White House last month to discuss a $10 million lawsuit against the late Alfred Bloomingdale, whose widow, Betsy, is a close friend of Nancy Reagan.

Presidential assistant Morgan Mason, who works in the White House political office, said he was acting on his own behalf when he met with Mitchelson and talked about the suit brought by Vicki Morgan, a 29-year-old model. She claims that Bloomingdale reneged on his promise to provide financial support and a house in return for her companionship.

Mason said he felt sympathy for Betsy Bloomingdale and "voiced my opinion" to Mitchelson that the suit was "an unfortunate situation" since it came as Alfred Bloomingdale was on his deathbed.

"Any normal, compassionate person would feel sorry that a man that ill was going through that kind of ordeal," he added. "The guy is deceased now. I felt it was kind of a sad thing for her Mrs. Bloomingdale to have to deal with."

The meeting with Mitchelson was held in the Old Executive Office Building in mid-August; Bloomingdale died of cancer Aug. 20 at age 66.

After the meeting, Mason and Mitchelson dined together and they have since talked about the Bloomingdale case by telephone, Mitchelson said yesterday.

Mason, who handles western political activity for President Reagan, said he didn't regret talking to Mitchelson from the White House. He said he has known the lawyer for years, since Mitchelson handled divorce proceedings for his mother, actress Pamela Mason. But, he added, he is sorry that the White House meeting has become "a big story."

White House deputy chief of staff Michael K. Deaver said Mason was "not acting on behalf of anyone but himself." Other officials said published reports that the White House is trying to pressure Mrs. Bloomingdale into a settlement of the case are "not true."

Mitchelson, a flamboyant attorney, argued the Lee Marvin case, which established the principle of palimony -- that unmarried couples who live together have a right to share their property when they break up. He said yesterday he is trying to expand that principle in the Bloomingdale case to include mistresses. Morgan claims she was Bloomingdale's "confidante and companion" for 12 years.

Bloomingdale, founder of the Diner's Club, got to know President Reagan through his wife's friendship with Nancy Reagan. Later, Bloomingdale became a supporter and contributor to the Reagan campaign.

Vicki Morgan's claimed relationship with Bloomingdale has made headlines for months in the nation's more sensational tabloids, but White House officials said they are not concerned that the case could embarrass the Reagans. Still, the officials were not pleased that Mason has focused attention on it by bringing Mitchelson to the White House.

Morgan claimed in her suit that Bloomingdale had reneged on an agreement to support her with $18,000 monthly and a house. She later sued Betsy Bloomingdale as well for interfering with her contract with Alfred Bloomingdale by stopping the checks when he became seriously ill.

After Bloomingdale's death, his widow was given court permission to defend the suit, and her lawyers recently asked Los Angeles Superior Court Judge Christian E. Markey to issue a summary judgment setting aside the lawsuits. Her lawyers have claimed that any promise of support and purchase of a house made by Bloomingdale was solely for Morgan's sexual services and thus an illegal "contract for prostitution."

Mason said yesterday it was not unusual for him to talk about the Bloomingdale case with Mitchelson. "He's my mother's divorce lawyer," said Mason, who is also the son of actor James Mason. "We've talked over many of his cases. He's done work for my family. It's not abnormal for me to comment on his cases. And he's had some unusual cases."

He described the White House meeting as "catching up" on matters of interest to both of them. "And when it the Bloomingdale case was mentioned, I voiced my opinion, my personal opinion. I said, look, this is kind of an unfortunate situation. And he didn't apologize . . . . "

Since then, Mason said, his talk with the lawyer has become "a big gossip thing," and now that it's become a "big" story "I'm sorry it's caused any problem at all."

White House officials described as inaccurate a report last week in the Los Angeles Times that he Reagans would like Betsy Bloomingdale to settle the lawsuit with an "appropriate" sum.

Mitchelson, reached by telephone yesterday, described the meeting at the White House as "cordial," but would not disclose specifically what was discussed.

"Morgan Mason called and I was happy to hear from him," Mitchelson said. "I see his mother in Beverly Hills. . . . We talked. He said he had been reading about the case in the paper and so forth and was following it with interest. And then I told him I was going to be in New York, and we got together."

Mitchelson said Mason had not issued a "summons" that he come to the White House to talk about the case. "It was an invitation," he said.

Asked whether he thought it unusual that a Reagan aide would call him to talk about the highly publicized case, Mitchelson said: "I don't think it was unusual considering that the Bloomingdales are friends of theirs the Reagans . Morgan Mason is the assistant for political affairs. Those are my own observations. I didn't inquire who sent for me or if anyone did. I didn't look behind my meeting with Morgan Mason to see if anyone was behind it or in front of it . . . "

In papers filed in Los Angeles yesterday, Vicki Morgan makes new claims about her relationship with Bloomingdale. She alleges that at one point he asked her to marry him, and that she was pregnant with his child but had an abortion. She also claims that Bloomingdale told her of his private feelings about influential people he knew, including the Reagans.

Morgan further said she was told of Bloomingdale's fund-raising activities on behalf of Reagan, and that, at Bloomingdale's urging, she worked in Reagan's Los Angeles campaign headquarters.