It was a classic move for Vornado Realty Trust’s chairman, Steven Roth: Just months after one of his chief competitors, Harry Macklowe, scooped up seven high-end office buildings in Midtown that Mr. Roth had lost in an earlier bidding war, Mr. Roth bought a chunk of the loans that Mr. Macklowe had secured to acquire the properties. If Mr. Macklowe paid off the loans, Vornado could rake in a return on its investment of as much as 10%; if not, the company would better position itself to buy the properties, according to people familiar with this strategy.

The $7 billion deal engineered by Mr. Macklowe last year has emerged as a symbol of the credit problems overflowing from the subprime market into the commercial market. In the highly leveraged transaction, Mr. Macklowe bought the seven sought-after Class A commercial properties by relying on his ability at the time to refinance the loans in a market where prices were continuing to rise. After the subprime crisis froze the credit markets, though, the developer was unable to refinance, and he is now working to hammer out a deal with the lenders to put the properties up for sale. An agreement has already been reached to put the signature General Motors Building on the block, and bids are due Friday.

For four of the other buildings, Vornado has emerged as a surprise stumbling block, turning its small investment into a powerful wedge. “Steve Roth is a very tough negotiator,” the editor of the real estate newsletter REIT Zone, Barry Vinocur, said. The newsletter was the first to report that Vornado was holding up negotiations. “He’s saying I can muck up this thing and maybe come out of it with some kind of gain,” Mr. Vinocur said.

While Vornado’s piece of the debt is small and is subordinate to more senior lenders, it does have power to block a deal between Mr. Macklowe and the lenders. Vornado has a 42% stake in two loans worth $158.7 million, or $66.4 million. The loans are secured by four buildings, including Worldwide Plaza at 835 Eighth Ave., 1540 Broadway, 527 Madison Ave., and Tower 56 at 126 E. 56th St.

Together with his son, William, Mr. Macklowe came to an agreement last week with the biggest lender, Deutsche Bank AG, which provided a $5.8 billion loan, to hand over ownership of the buildings while retaining some management position. But Vornado went “radio silent” and refused to sign off on the deal, Mr. Vinocur said. As a result, the loans went into default and Mr. Macklowe was served with papers that started the process of foreclosure.

Mr. Macklowe is also negotiating with Fortress Investment Group over a $1.2 billion loan that was due this weekend. Mr. Macklowe put up the GM building as collateral for the Fortress loan, and while the discussions with the lender aren’t finalized, an agreement has been reached to sell the property.

Executives at Vornado, Deutsche Bank, and Macklowe properties declined to comment for this article.

Vornado’s acquisition of Mr. Macklowe’s loans last summer “was a strategic investment,” the director of the real estate research firm Real Capital Analytics, Daniel Fasulo, said. “Vornado is pursuing an angle in this that is in their best interest; we just don’t know what it is yet.”

One possible strategy is for Vornado to use its seat at the negotiating table to acquire all the debt from the other lenders and refinance these loans, giving it an avenue to owning the real estate. Vornado is not short on cash, and would be able to finance such a deal with partners, sources familiar with the company say.

“In the end, it’s about Steve Roth putting pressure on Macklowe and wanting to get a hold of the properties somehow,” a source said.

If Vornado chooses not to buy up all of the loans, it could proceed by “injecting chaos” into the negotiations by refusing to come to an agreement, Mr. Vinocur said. This delay could drive down the value of the debt, allowing Vornado to buy up more mezzanine loans from other subordinate lenders. Then, when the value of that debt rises down the road, Vornado could sell it off at a modest gain.

Another option is simply for Vornado to use its ability to block a deal to negotiate a cash payment to offset its loss.

What is clear is that Vornado is taking a path that is riskier than simply writing off the $66.4 million. In addition, as the commercial market continues to decline, the value of the real estate will decrease and because Vornado is a junior lender, it will be paid only after the more senior lenders are paid, with the possibility there won’t be enough money to go around.

This risk is nothing new to the real estate investment trust. In fact, unconventional choices have characterized Vornado from its inception. It often buys stakes in distressed companies that have significant real estate holdings, including Sears, Toys “R” Us, and Alexander’s. When these companies scaled back the number of stores they had, Vornado snatched up the real estate and redeveloped it.

“Steve Roth is the king of extracting real estate value from unexpected places,” another source, who spoke anonymously because of the sensitivity of the ongoing negotiations, said.

This is also not the first time the company has made a foray into these types of loans. One reason these loans are attractive, the chairman of the real estate firm Massey Knakal, Robert Knakal, said, is that it allows REITs such as Vornado to have access to information in the company that is not always public. “They are strategic investments; they position a buyer ahead of other buyers down the road.”