What better place to take royalty than though the majestical ambiance of Washington art galleries on a glorious fall day?

And so yesterday, as part of the official visit, the first lady opted to stop by the grand East Building of the National Gallery with Queen Sofia for a leisurely stroll and viewing.

As official visits go, it was about as leisurely as logistically possible.

Nancy Reagan and Queen Sofia hopped in a limo followed by a three-car motorcade, nine Secret Service agents, four advance men, three members of the first lady's staff and the queen's military aide.

At the museum, they strolled and viewed for 45 minutes with all of the above, and with 11 other ladies, four curators, a bevy of the gallery staff, several reporters and 31 photographers and cameramen who showed up behind ropes in every third room.

"Why are they just [showing up] here in some places?" inquired the queen, as the flashes and the television lights trained on her.

"Because they are only allowed in certain places," responded gallery director 4. Carter Brown.

"Oh. I thought maybe there was something special to look at in these rooms," smiled the queen.

"Yeah, YOU," said Brown. Everyone laughed.

Brown did most of the talking through most of the tour. He was relieved at various stops by several of the gallery's curators who are experts on certain exhibits.

The first ladies seemed properly impressed at the right places. Rodin and Picasso were quite popular, and they listened intently to Brown. At one point, for an awkward moment they couldn't decide who should sign the guest book first. They giggled and then the queen obliged at Nancy Reagan's insistence. "Mine looks so plain," observed the first lady. The queen scribbled a more fancy signature.

Both women were exquisitely dressed. A purple suit with perfectly matched silk ruffled blouse for Nancy Reagan. The purple pumps with tiny purple tuxedo bows blended in nicely. There was also a purple pocketbook.

Queen Sofia wore a black jacket, black pumps, a black-and-brown plaid skirt, and gold rings and bracelets.

At the end everyone kissed everyone else goodbye. Except for Pam Brown, wife of J. Carter. She curtsied.

Meanwhile, across town, Juan Carlos stopped by the Capitol at noon to dine with Senate and House leaders. The lunch was closed to outsiders.

Another group of about 30 cameramen and a few reporters were herded into a tiny Capitol office to catch a glimpse of the king with the leaders. Asking questions was out of the question.

"I love your country," House Speaker Thomas (Tip) O'Neill (D-Mass.) was heard saying. The reportters wrote this down.

At the insistence of the American press, protocol aide Mary Masserini allowed that one member of the Washington press corps and one from the Spanish group could enter the luncheon room for two minutes.

"We're going to pool it," she informed the 11 non-English-speaking Spanish reporters. Blank stares. Finally, one member of the group figured it out and translated. They decided to play guess-the-right-number to see who went in to write down the color of the napkins and watch the king take his first bite of melon draped in prosciutto.

Dos won.

One thousand people were invited to the Corcoran Gallery last night by Spanish Ambassador Jose Llado to shake hands with the king and queen at the opening of the "Spanish Art Tomorrow" exhibit; 2,800 people showed up.

The receiving line streched from the street through the main foyer, up the grandiose staircase, around the balcony, and emptied at the royal feet.

Overwhelming it was, but as National Theatre board chairman Maurice Tobin so aptly put it, "This is a very good list."

The king was a big hit with the ladies.

"I told him, 'You may be a king, but you're Prince Valiant to me,'" sighed one guest.

"He's so charming and wonderful," gushed Peggy Donovan, whose husband was once head of the American military mission in Spain. "He kissed me when I went through the line. I think he was just so happy to see a familiar face."

The faces, familiar and unfamiliar, included a cross section of Washington's socially "in" group, ambassadors from most of the Latin and Hispanic nations, and officials from the executive, judicial and legislative branches: Secretary of State Alexander M. Haig Jr. and his wife, Patricia; presidential counselor Ed Meese; Supreme Court Associate Justice Sandra D. O'Connor, and Sen. Strom Thurmond (R.S.C.). They all were allowed to cut in line.