If it all comes off according to plan, there will be a super gathering of stars and political celebrities gathering in New York City April 19 to celebrate the 70th birthday of former senator Eugene McCarthy, the man who wanted to be president. But then, remembering how disorganized his presidential attempt was, McCarthy isn't exactly certain who will show up at the Congregation Rodeph Sholom synagogue. He joked yesterday that there seems to be a birthday party scheduled "every weekend on into next year."

McCarthy, who now lives out in Woodville, Va., and enjoys being referred to as the "sage from the Rappahannock," actually observed his 70th birthday Saturday; and there will be a party for him April 12 at the Georgetown Club with the idea of bringing together a number of his pals from the years he served in the House and the Senate. The invitation list for the New York party (it will be called "A Reunion of the Class of '68," in reference to his primary campaign that helped end President Johnson's career), includes such names as actors Paul Newman, Dustin Hoffman, Carroll O'Connor, Warren Beatty and Shirley MacLaine and singer Joan Baez; former California governors Edmund G. (Pat) Brown and Jerry Brown and columnist William F. Buckley.

McCarthy says that reaching 70 makes him a "patriarch." As for the note included in the New York invitation, emphasizing McCarthy had no plans for 1988, he joked, "I didn't subscribe to that" -- and mentioned a few other political patriarchs such as Churchill, Adenauer and De Gaulle. As for whether the conflict in Nicaragua could be his campaign issue to replace Vietnam, he said with a laugh, "I don't know. Vietnam was 15 years old before we made a judgment on that. We don't want to make any snap judgments on Nicaragua, since it is only two years old." McCarthy has completed the manuscript on a book he refuses to call a memoir, tentatively titled "Up to Now." It is scheduled to be published by Harcourt Brace Jovanovich in the fall. End Notes

Indian Ambassador K. Shankar Bajpai spent his last day at his post yesterday and in the evening was the host of a farewell party at his residence on Macomb Street, where he spent part of his youth. Bajpai, a 1944 graduate of St. Albans School, lived there when his father was ambassador during World War II. Yesterday Bajpai also turned 58, the mandatory retirement age in the Indian civil service. A new ambassador has yet to be named. Among the guests expected last night were Attorney General Edwin Meese, Supreme Court Justice Sandra Day O'Connor, Chief of Protocol Selwa Roosevelt, FBI Director William Webster and Ambassadors Allan Gotlieb of Canada and Wilhelm Wachtmeister of Sweden . . .

The National Gallery continues to attract the stars. Most of the cast and crew of "Long Day's Journey Into Night" took advantage of their day off yesterday to visit the Impressionist show. Jack Lemmon, his wife Felicia Farr and costars Peter Gallagher, Kevin Spacey and Bethel Leslie were with the group . . .

Former congressman John Jenrette, who is serving a two-year sentence for bribery and conspiracy in connection with the FBI's Abscam sting operation, was disbarred yesterday by the South Carolina Supreme Court . . .

Five years ago on March 30, Robert F. Bonitati, a special assistant to President Reagan, was leaving the Washington Hilton ballroom with the president and Press Secretary Jim Brady when public relations consultant Victor Kamber delayed him in conversation. The president and Brady reached the street and the waiting John Hinckley shot and wounded both men. Bonitati has often said his brief conversation with Kamber may have saved his life. Now, five years later, Bonitati, who was the president's liaison with labor, has left the White House to join the Kamber Group as a vice president for public affairs . . .

Frank Hodsoll, chairman of the National Endowment for the Arts, will be one of six people to receive honorary degrees from the University of Massachusetts tomorrow at a ceremony observing the 10th anniversary of the university's fine arts center. He will speak at the event. Joseph Duffey, former chairman of the National Endowment for the Humanities, is the chancellor of the University of Massachusetts. Others receiving honorary degrees are comedian and television personality Bill Cosby, an alum of the university; Bruce MacCombie, composer and new dean of the Juilliard School of Music; Billy Taylor, jazz pianist, composer and conductor; Lois B. Torf, art collector and patron; and Graham Gund, architect and art collector . . .