If that bar stool Jason Robards is sitting on in the Kennedy Center production of "The Iceman Cometh" looks familiar, it probably is. The setting for the Eugene O'Neill classic is Harry Hope's gin mill, and Nathan's bar in Georgetown donated its bar stools for this production, which will run Aug. 10 through Sept. 14. Since "Iceman" is a grueling four-hour show, there will be only six performances a week, eliminating the usual Thursday and Saturday matinees . . .

It's too bad it's only for one day -- on Thursday, Third Street in front of the Capitol's West Front between Independence and Constitution avenues will be renamed Sesame Street. Mayor Marion Barry and Education Secretary William J. Bennett have been invited, and the mayor's son Christopher and his classmates from Tots Nursery School are expected to show up for the publicity event for Big Bird, who will be there to promote his first movie, "Follow That Bird" . . .

New York Gov. Mario Cuomo was surprised to learn that he has been picked as one of the 10 sexiest men in the nation by Playgirl magazine. He was part of a list that included Rep. Jack Kemp, actor Don Johnson, "Nightline" anchorman Ted Koppel and dancer Alexander Godunov. Cuomo said he didn't know what the honor meant and pointed out that his wife Matilda was not on the Playgirl selection jury . . .

In the sake of fairness in covering beauty contests, Summer Simmons, a 29-year-old California mother of one, was crowned Ms. Nude International (U.S.A.) Sunday night. And all she wore was her crown. She was selected on the basis of face, figure, personality, overall suntan, poise and philosophy of nudism. And she won't have to relinquish her crown if undraped photos of her appear in Penthouse magazine . . .

Several weeks ago there was a conference in Barcelona that included a number of Washington journalists and a group of former White House aides from several administrations. Among the aides were George Reedy, Gerald Rafshoon, Ron Ziegler and Dave Gergen. The moderator asked each to speak for 20 minutes before taking questions. Former Richard M. Nixon press secretary Ziegler interrupted, "They can talk for 20 minutes; I'll be talking for 18 1/2 minutes." The Spanish students didn't get it but the Washingtonians broke up. Someone should have explained to the students that you had to have been there . . .