London Mayor Boris Johnson (left) tours several exhibits within the Smithsonian National Air and Space Museum in Washington, D.C. on February 12, 2014. AT RIGHT is Peter Jakab, Chief Curator of the museum. (Photo by Marvin Joseph/The Washington Post)

London Mayor Boris Johnson toured the National Air and Space Museum with its chief curator and other Smithsonian officials Thursday as part of an ongoing effort to woo the American museum to open its first gallery outside the United States.

“We’ve come to gawk,” the publicity-friendly Johnson said after looking at various exhibitions, including the Wright Flyer and a video of President John F. Kennedy’s 1961 vow to send an American to the moon. “This is the greatest museum in the world. It is an absolute cathedral to American achievement.”

The tour came during two days of meetings between the parties to work out the terms of the agreement first announced last month. Johnson and the London developers who are remaking the former Olympic park into a cultural complex have pledged $50 million to secure the Smithsonian’s participation.

The complex would include space for the Victoria and Albert Museum, Sadler’s Wells Theatre, University College London East and the University of the Arts London. It is projected to open in 2021.

There is no deadline for the deal, said Al Horvath, acting Smithsonian Secretary. “We are moving along. We still have work to do,” he said.

Meanwhile, the Smithsonian is forging ahead to prepare for the potential facility. Richard Kurin, the Undersecretary for History, Art and Culture, has been charged with the programming of the site. Board of Regents Chairman John McCarter said the move was part of the institution’s effort to galvanize support.  “We want to build involvement, build consensus in all directions,” McCarter said.

Julian Raby, the director of the Arthur M. Sackler gallery and the Freer Gallery of Art is rumored to be the front-runner to lead the London venture. McCarter did not refute that, saying coyly that “Julian has been involved from the start.”

While both expressed optimism, neither Horvath nor Johnson would guarantee the project will happen.

“It’s important not to count our chickens here. We hope to continue the talks to fruition,” Johnson said, adding that the chief concern is to ensure there will be no costs to taxpayers of either country. Smithsonian officials estimate it would cost about $7 million annually to operate, money they say would come from private sources.

If an agreement is reached, it would mark the first time in the Smithsonian’s 168-year history that it would have a public presence outside the United States. The institution has research centers around the world, but its public galleries are limited to New York and Washington.

A design competition is underway, but there are still no details about the building and the physical relationship between the various organizations. The Victoria and Albert Museum would get the largest space, the developers confirmed, while the Smithsonian’s portion is expected to be abut 40,000-square feet, about half the size of the main hall of Air and Space.