Orchestrating the portrayal of the First Family apparently is becoming a White House must.

At two gala art openings last week, Reagan aides imposed tight restrictions on when, where and with whom the president and first lady could be photographed. At the Metropolitan Museum of Art opening for "The Vatican Collections: The Papacy and Art," Nancy Reagan was skillfully kept away from nude sculptures--at least when someone might snap her picture looking at them.

Later in the week, when multimillionaire art collector Paul Mellon gave 93 works to the National Gallery of Art, it wasn't too few clothes that worried the White House but too many that cost too much.

Aides made certain there was no photo opportunity outside the white-tie dinner in the NGA Rotunda that could show Nancy Reagan with Bunny Mellon in their designer gowns, and the president with Mellon in white tie and tails. The president himself was scheduled to announce Mellon's gift to the American people--private sector initiative in its purest form.

As two veterans of the U.S. cavalry, Reagan and Mellon could hardly miss hitting it off. They talked about horses, laughed at each other's jokes and left a few in the well-to-do crowd suspecting that it is only a matter of time before Mellon invites Reagan out to his Upperville, Va., farm for a little gallop de deux.

But press arrangements became so confusing that even National Gallery officials didn't know until shortly before the Reagans arrived that no pictures would be allowed of them being met by the Mellons, or of the two couples touring the newly presented collection.

"The White House said they had some problems with the folks at the museum," explained one frustrated wire-service photographer in the president's traveling press pool.

Reagan aides told Gallery officials a somewhat different story. "It was called 'a political decision,' " said a source privy to the White House ultimatum.