Eleven years ago, when Gannett left Rosslyn for Tysons Corner, Malcolm Schweiker helped broker the deals to fill Rosslyn’s “twin towers,” which at the time was the premier property in the portfolio of developer Stanley I. Westreich.

Now that portfolio, in the hands of Westreich’s son Anthony, has another preeminent property: the 390-foot office tower being constructed at 1812 N. Moore St. And last week Anthony Westreich again hired Schweiker and his broker team at CBRE to fill the space.

Monday Properties typically handles much of its leasing in-house. Westreich, chief executive of New York-based Monday Properties, had developed intimate knowledge of his portfolio from working for his father and leasing the properties himself. He said every lease in the 11 Arlington office buildings the company owns was negotiated either by himself or his brother-in-law, Timothy Helmig, who heads Monday’s Washington office.

Nevertheless, Westreich said the company has long relied on contracted brokers to help with major leasing projects such as the 580,000-square-foot Rosslyn project. “We have six-and-half million square feet of office space and we do our own leasing, however whenever we have a large block of space available we always use a co-broker,” Westreich said.

Monday and partner Goldman Sachs are committed to completing the building, whether or not some of the cost is financed — something nearly every office developer requires. “We’re still talking to lenders. We’re committed to moving forward all equity and we are in the market for construction financing,” Westreich said.

Construction workers on the site at 1812 N. Moore St. in Rosslyn. When completed, the office tower is to be 390 feet tall. (Jeffrey MacMillan/Capital Business)

Construction is a few weeks ahead of schedule, he said, and will be ready for interior build-out a year from now.

The market for tenants to lease the space, however, has slimmed considerably since Monday began construction. Compared with the first quarter of last year, the Washington area in the first quarter of 2012 showed a 65 percent drop in leasing activity, from 10.7 to 3.7 million square feet.

Schweiker, who will market the building along with Ed Clark and Mark Klug, said he envisions filling 1812 N. Moore with a mix of associations, lobbying groups, financial services firms and perhaps a law firm. Ten years after the Gannett deal, he said the opportunity for high-end space meant companies would be moving back to Rosslyn, and he said the Silver Line Metro extension could help.

“As much as everyone is talking about the advantage of Metro moving west, we look at it as an opportunity to bring workers back in,” he said.