The hand-lettered sign posted in the hallway outside the Oval Office reads "No Tours," but there has been plenty of traffic at the White House in recent days.

Yesterday at 11:45 a.m. it was Rep. Herbert E. Harris II (D-Va.), sporting a green-and-white Carter-Mondale button, who was ushered into the President's office to endorse Jimmy Carter's bid for a second term.

For fully three minutes, the president and the congressman, who bear two of the widest grins in town, beamed before two dozen photographers and reporters, and traded lavish phrases such as "my very good friend" and "this dynamic leader."

Ten minutes later, precisely at 11:55 a.m., freshman Rep. David E. Bonoir (D-Mich.) walked into the Oval Office, playing his role in Carter's "Rose Garden strategy" by endorsing the president.

Because similar dramas have been played out more than a dozen times in recent weeks in either the Oval Office or the Cabinet Room, it was understandable that not all of the dignitaries were easily recognized.

One Carter aide yesterday referred to the Northern Virginia congressman as "Hubert Harris" and members of the press corps later mistook a visiting foreign diplomat for another Carter supporter.

The endorsement ritual calls for the endorsee to stand next to Carter, accept words of praise for his or her decision to back the president, and then return the compliments, as cameras click and reporters scribble notes.

The president singled out Harris' sponsorship of the $1.7 billion Metro rail financing bill as an illustration of Harris's leadership, ignoring the fact that his administration opposed the congressman's bill until its passage seemed assured.

Carter also lauded Harris as "a responsible spokesman for the civil servants" who comprise so much of Harris's constituency. Owash in such praise, Harris declared the moment "one of the highlights of my life," and revealed not only his political support but "my personal affection to you and to Rosalyn."

Harris, who said last month that he wasn't likely to make an endorsement because "I make the laws and let the other folks pick the president," said yesterday that the president's "quick and firm movements" regarding Iran and Afghanistan helped win his support.

Fingering a Carter-Mondale button on his lapel, Harris concluded: "This country needs Jimmy Carter as president."

Carter continued what passes for "a meaningful colloquy" in political circles by replying that his rapport with Harris typifies "the close relationship" between the White House and many members of Congress.

The President said Harris's "frequent town meetings" in Fairfax county and Alexandria have served as "a sounding board" for federal employees to express their views. "Keep it up so you and I can both be better servants," the president concluded.

The fast-talking Harris got in the last words, thanking the president for allowing "Scotty Campbell [Alan K. Campbell, director of the Office of Personnel Management] to subject himself" to the often critical questions of federal workers at Harris' forums.

Before anyone else could get a word in, a presidential aide snapped "lights" to the television crews, meaning shut them off, and "out" to the reporters, who departed mumbling about the saccharine exchange.

A Carter campaign aide said Harris's endorsement -- the 110th by a House Democrat -- is important because he represents an area which, with its many liberals and federal employes, is likely to be a stronghold of Carter's chief rival for the nomination, Sen. Edward M. Kennedy.

Virginia delegates to the Democratic National Convention are selected after a series of meetings that begin March 22.

The endorsement routine at the White House winds up with the endorsee talking to the news media for a second time on the driveway just outside the west wing.

Harris held the attention of the reporters and photographers there for a few minutes, until Bonoir took his place. Then a third man appeared, but because he was not recognized, a reporter thrust a microphone in his face and asked, "who did you see and what did you talk about?"

The startled visitor replied in a German accent that he had been discussing world events with Zbigniew Brzezinski. The reporters were too embarrassed to ask his name, but later learned it was West German finance minister Walter Kiep from Lower Saxony.