Developer Larry Silverstein, who earlier this year agreed to surrender some of the 10 million square feet he controlled at or around ground zero, is back in acquisition mode in Lower Manhattan.

The 75-year old developer, who will build and control much of the former World Trade Center site, is close to finalizing a deal worth more than $150 million to buy an 11-story office building at 99 Church St. from Moody’s Investor Services, The New York Sun has learned. The deal would be a partnership between Silverstein Properties and the California State Teachers’ Retirement System according to sources familiar with it.

The building at 99 Church St., which contains about 300,000 square feet of office space, is just north from where the Mr. Silverstein is planning to build and lease three soaring commercial towers containing a total of 6.2 million square feet of space. It is about a block from 7 World Trade Center, Mr. Silverstein’s new 52-story office building, which opened in May, and three blocks east of the site where Silverstein Properties has started to build the 1,776 foot Freedom Tower for the Port Authority.

Mr. Silverstein owns office buildings in Lower Manhattan at 120 Broadway and 120 Wall Street, leading some observers to jest that he so dominates the neighborhood that it ought to be known as “Silverstein-stan.”

Silverstein Properties leased the World Trade Center from the Port Authority six weeks before it collapsed.

During negotiations earlier this year over the redevelopment of the former World Trade Center site, Mr. Silverstein clashed with the city and the Port Authority over contrasting predictions on the future of the downtown office market. In recent months, Mr. Silverstein’s optimistic forecast seems to have been prescient, as demand for office space in Lower Manhattan is strong, and rents are approaching highs not experienced since the late 1990s.

Now, Mr. Silverstein appears to be upping his ante.

The president of the Real Estate Board of New York, Steven Spinola, said the purchase of 99 Church Street would be “another indication of Larry’s confidence and commitment to Lower Manhattan.”

“He is looking to have a bigger percentage of the total market down there, which is now clearly moving in the right direction, based on his deals,” Mr. Spinola said.

About 100,000 square feet of additional air rights are available on the site, which is at the corner of Barclay and Church Streets, just to the east of the Woolworth Building. Sources familiar with the deal said the developer could choose to add space on top of the existing building, convert it to residential apartments or a hotel, or demolish it and build new.

A director for Real Capital Analytics, Daniel Fasulo, said the price — at around $400 a square foot — is much higher than he expected for the building, constructed in 1952. He said the developer would likely wait and let the market dictate what he does with the property.

“The people on the ground, like Silverstein, are very bullish on office,” Mr. Fasulo said.

“Developers like to control their own little submarkets, and Silverstein certainly has an interest in that area,” Mr. Fasulo said. “He will know what tenants are interested in that submarket, and he will have another option for them at a lower cost.”

Moody’s is selling its building to become Mr. Silverstein’s biggest tenant at 7 World Trade Center, taking 15 stories, or 600,000 square feet of new office space.

The president of the Downtown Alliance, Eric Deutsch, said it was a good sign that a private developer like Mr. Silverstein is continuing to invest in Lower Manhattan. He said that the site along Church Street, where hundreds of thousands of square feet of retail stores and the new PATH station are planned, would become a new nexus of activity when redevelopment plans are completed.

“Church Street is the position to regain the retail hub we had at the Trade Center, and do it in a newer and more lively manner,” Mr. Deutsch said. “That is really the portion of the site that will be the most enlivened with activity.”

A spokeswoman for Moody’s and a spokesman for Silverstein Properties declined to comment.

In October, Silverstein Properties, also in partnership with the California State Teachers’ Retirement System, purchased 575 Lexington Avenue, a 35-story, 600,000-square-foot tower at 51st Street, for $400 million, or about $665 per square foot.