AOL is moving its headquarters to New York City from Dulles, Va., part of a strategy by the Internet division of Time Warner Inc. to transform itself into a Web company supported by revenue from digital advertising — similar to larger rivals Yahoo! Inc. and Google Inc. — rather than online subscription services.

“New York City is the center of advertising, so it makes perfect sense to locate our corporate headquarters here,” the chairman and CEO of AOL, Randy Falco, said in a statement announcing the move yesterday.

The company, which has had its headquarters in northern Virginia since its founding in 1985, inked a 15-year deal for more than 152,000 square feet on the entire fourth and fifth floors of 770 Broadway, a 15-story building at Astor Place where retailers Kmart and Ann Taylor have stores. Work has already begun on the office space and occupancy is expected this spring. Asking rents for buildings in the neighborhood are $50 to $60 a square foot, brokers say.

AOL, which merged with Time Warner six years ago, has been struggling as more Internet users switch to broadband from dial-up. Last month, Time Warner reported that AOL’s second-quarter sales dropped 38%, to $1.3 billion, as it lost 1.1 million paying subscribers. It has tried to combat these losses by turning to online advertising revenue and driving traffic to its sites by giving away AOL.com e-mail accounts, software, and other features once reserved for paying customers. In the second quarter, its advertising sales gained 16%.

While the AOL-Time Warner merger was hailed at the time as creating one of the largest press and broadcast powerhouses, AOL this year will represent just 11% of Time Warner’s overall company revenues and 14% of its operating earnings. Analysts have long suspected that the two entities will split, and AOL’s decision to move to Greenwich Village rather than into Time Warner’s headquarters at Columbus Circle may be seen as further evidence.

“AOL is a troubled property, and I anticipate a future time when the two will separate,” the principal analyst at the Enderle Group, Rob Enderle, said.

AOL went to pains yesterday to say that all 4,000 workers located in Dulles will remain on staff, and that only its senior executives — it would not provide specific number — would relocate to New York City. In addition, the 400 AOL employees currently located at 75 Rockefeller Plaza will also be moved into the new downtown office space, it said.

The brokerage firm Staubach, which represented the company in its lease at 770 Broadway, recently began marketing two floors, or 54,000 square feet, at 75 Rockefeller Plaza. The 33-story building, at Fifth Avenue and 50th Street, was the headquarters of Time Warner before it built its Columbus Circle site, and the company still occupies a large portion of the building. Staubach declined to comment, citing a confidentiality agreement with AOL.

“Our programming and advertising people are already in New York, at 75 Rock, and we will move them over to the new space,” an AOL spokeswoman, Anne Bentley, said. “All the product development people for things like AOL e-mail will stay in Dulles.”

Still, there will likely be some downsizing in Dulles as employees decline to relocate.

Yesterday, the company also announced the creation of Platform A, a new online network that will sell advertisers targeted ad space on AOL’s Web sites. The new entity will integrate many of the company’s recent acquisitions, including German-based ADTECH, the Boston-based mobile phone ad network Third Screen Media, and the Manhattan-based firm Tacoda. A former Tacoda CEO, Curtis Viebranz, will head up Platform A.

“With the increasing fragmentation of online audiences, the best way to serve advertisers is to enable them to harness massive advertising networks that reach across the entire Internet,” Mr. Falco said. “Over the past eight months, we have put together a network with unprecedented reach and state-of-the-art solutions that accomplishes this.”

The company also announced that it has formed a partnership with Hewlett Packard Co. to offer co-branded, local versions of its portal site, tool bar, and search capabilities on HP desktops and notebook personal computers.