From starvation to a $5,000-a-plate dinner: Mitch Snyder, the nation's most visible activist for the homeless and the hungry, is bringing his movement uptown where the money is. With the CBS television movie "Samaritan: The Mitch Snyder Story" scheduled for showing May 19, Snyder is organizing a celebrity-studded fund-raising gala for May 12. He's even using the volunteered, bipartisan expertise of Joe Canzeri and Gretchen Poston, two of the city's better known events organizers.

At a press conference next Thursday, Snyder and Mayor Marion Barry will announce some of the details of the gala, which is designed to help raise the $2.5 million Snyder's Center for Creative Non-Violence needs to remodel its shelter at Second and D streets NW. The residents of the shelter will see the film there that afternoon at a party donated by Ridgewell's Caterers Inc.

The rest of the day includes a $5,000-a-plate dinner donated by and held at Dominique restaurant, where guests will have an opportunity to dine with Snyder; the man who plays Snyder, Martin Sheen; and actress Valerie Harper, who with Dennis Weaver heads LIFE (Love Is Feeding Everyone), the organization cosponsoring the day's activities. Weaver is also expected to be in town. Then in the evening there will be the premiere showing of "Samaritan" at the National Theatre and a reception in a large tent on Western Plaza in front of the theater.

And to show how uptown the evening will be, the cosponsors range from socialite Jennifer Phillips and Eunice Shriver to Sens. Mark Andrews, Thomas Eagleton, Carl Levin and Howard Metzenbaum; the Kennedy Center's Peter Sellars; Motion Picture Association of America President Jack Valenti; television producer Nancy Dickerson; and Capital Centre owner Abe Pollin. After getting involved in the organization of this gala, Snyder said he wishes "I was back on the heat grate. Life was simpler there. All I had to worry about was being warm and dry." Iacocca Ties the Knot

Chrysler Corp. Chairman Lee Iacocca, who usually does things with dramatic, public flair, was quietly married yesterday in a private ceremony at St. Patrick's Cathedral in New York City. The 61-year-old Iacocca married Peggy Johnson, 34, a New York advertising executive, in the Cardinal's Chapel with only two close friends in attendance. His daughter Kathryn said yesterday that she attended a wedding brunch after the ceremony. The couple had been engaged since January 1985.

There were few details about the wedding or who was there. The announcement came in a three-paragraph news release from the Chrysler Corp. that said, "The Iacoccas left New York on a wedding trip." Iacocca's first wife, Mary, died of complications from diabetes in 1983. Washingtonians may get an opportunity to meet the couple next week. Iazocca is expected at the Convention Center Tuesday for a Chrylser auto show.

Iacocca did get the jump on his daughter's engagement announcement, which is scheduled for this weekend. Kathryn Iacocca, 26, president of the Iacocca Foundation, a philanthropic organization dedicated to funding diabetes research, is engaged to marry Ned Carlton Hentz, 28, who works for the New York advertising firm of Batten, Barton, Durstine & Osborn. A June wedding is planned in Bloomfield Hills, Mich., after which the couple will reside in Manhattan. Kathryn Iacocca was briefly engaged to Jeff Harper, an executive vice president with the Canzeri Corp. here.