World middleweight boxing champion Marvelous Marvin Hagler and former world welterweight champion Sugar Ray Leonard would never meet in the ring but they were to sit down and share a couple of steaks last night at Jameson's, a new Bethesda restaurant owned by Leonard along with Mike Trainer, Leonard's attorney-business manager; Glenn Brenner of WDVM-TV; and three area businessmen, John Cralle, Dan O'Connor and Marty O'Connor . . .

With the Treasure Houses of Britain still packing them in at the East Building of the National Gallery of Art, "The New Painting: Impressionism 1874-1886" opens Friday and all the tickets for the first two weekends are already reserved. To kick off the exhibition, which will be bringing long lines to the West Building of the National Gallery through April 6, a black-tie Trustees' Dinner will be held tonight in the rotunda with a guest list that includes former senator Howard Baker, Chief Justice Warren Burger, Mayor Marion Barry, Sens. Mark Hatfield and Charles McC. Mathias Jr., Rep. Jack Kemp, Kennedy Center Chairman Roger Stevens, Secretary of Defense Caspar Weinberger, artist Jamie Wyeth, actress Sophie Renoir (great-grandaughter of Impressionist artist Auguste Renoir), and the ambassadors of Britain, Italy, Spain, Germany, Korea, Singapore, Switzerland, Australia and France . . .

Merrie Spaeth, a former special assistant to President Reagan and director of media relations at the White House, will become executive vice president in the Dallas-based public relations and media consulting firm of Fairchild/LeMasters Inc. Spaeth, who also writes a financial column for USA Weekend magazine, had been a vice president-public affairs for RepublicBank Corp. since leaving the White House . . .

Singer Kate Smith, the woman who owns "God Bless America" and who costarred with actor Ronald Reagan in one of her two movies, received a telegram from the president wishing her a speedy recovery. Smith, who appeared with Reagan in the 1945 movie "This Is the Army," had her leg amputated Sunday in Raleigh Community Hospital, Raleigh, N.C. . . .

Stephanie Kenyon Beehler, a fine arts appraiser and auctioneer at C.G. Sloan & Co., was among the 10 outstanding young working women in America selected by Glamour magazine. The 10 women stopped by the White House Monday to meet President Reagan . . .

Sometime presidential candidate Jesse Jackson walked into the Jennifer Street Restaurant yesterday to ask owner Bob Young if this was the place to get "Momma Young's Chicken Soup." Jackson, who had come in with CBS News correspondent Bob Schieffer from the CBS offices next door, was told the soup wasn't ready. Young made some up and delivered it to the news offices . . .

World famous gourmet cook and actor Paul Newman has given away some more of his food profits. This time it's $25,000 from the sale of his various popcorn, spaghetti and salad dressing sales to Missionary Vehicle Association Inc., a Washington-based charity that provides tough, rugged vehicles to American missionaries working in developing countries. Newman, who gives away all his food profits to charity and has just developed a microwave popcorn, gave $18,000 to the same association last year. The present gift will buy a Jeep for a brother in South Korea, a station wagon for a nun in Ghana, a pickup truck for a priest in Tanzania, a motorcycle for a priest in Bolivia, a truck for a priest in Namibia, a station wagon for a priest in Papua New Guinea and a pickup truck for a priest in Liberia . . .

Peter Sellars and Andy Warhol -- now that's a combination to contemplate. Sellars, artistic director of the American National Theater at the Kennedy Center, who has a different way of looking at things, sees Warhol as a robot and has a long-range project to produce a one-man robot show based on Warhol's words of wisdom. The fact that the technology does not exist yet to have a robot wearing a Warhol mask on stage ad libbing and saying different things at every performance, of course, doesn't faze Sellars. He's working on the show, which he doesn't expect to complete for at least five years . . .

San Francisco Examiner editor David Burgin, formerly of The Washington Star and most recently of the Orlando, Fla., Sentinel, is leaving the paper he was brought in to spruce up not long ago. Publisher William R. Hearst III said yesterday that he will assume the title of editor.