Sales of U.S. office buildings in the second quarter fell 10 percent from a year earlier to $14.8 billion, according to Real Capital Analytics, which tracks sales of office properties of at least $2.5 million.

Corporations are reluctant to hire because of uncertainty over the U.S. deficit, changes in tax policies, and the effect of Europe's debt crisis on the United States. Buyers of office buildings have become nervous about the future due to weak job growth, which drives leasing and in turn rent.

"One of these issues by themselves is not going to move the dial," said Dan Fasulo, Real Capital Analytics managing director. "Add everything up, and it's really hard to make a $100-million decision in that type of environment."

U.S. office prices rose 2.5 percent in May, the most recent date for which figures were available. As of end-May, they were 8.9 percent higher compared to a year ago, according to Moody's/RCA Commercial Price Indices.

"There's been a little bit of a pause in terms of core buyers investment activity as they look to get a little bit more value in their acquisitions," said Sonny Kalsi, the former co-head of Morgan Stanley's Real Estate Investing.

Kalsi is the founder of GreenOak Real Estate Advisors LP, which is raising about $300 million to buy office buildings, according to alternative asset research firm Preqin.

U.S. Securities and Exchange Commission rules do not allow those raising money to comment on on-going fundraising.

Using debt financing, GreenOak will be able to buy about $1 billion of buildings. It will target those that need leasing and capital improvements. The buildings will primarily be located in New York, Boston, San Francisco and Los Angeles.

Kalsi said many investors are in no rush to buy.

"Ultimately the deal falls apart not because investors think it won't get leased up, it just becomes a question of how long they think it will take to get leased and what the rents are," Kalsi said.

Blackstone Group LP (BX.N), one of the world's largest owners of real estate, is in no hurry to sell large chunks of some its vast office holdings it bought in 2006 to 2007.

"Over the next couple of years we'll sell," Jonathan Gray, senior managing director and global head of real estate at Blackstone, said at the CNBC Institutional Investor Delivering Alpha Conference in Manhattan. "I wouldn't expect to see anything too quickly," he added.

At the end of the second quarter, the national vacancy rate stood at 17.2 percent, flat with the prior quarter, according to real estate research firm Reis Inc.

Yet, there were markets where leasing and rent growth was strong and sales have followed suit.

The technology/social media sector of the economy continued to outperform many of the other sectors over the past year. Six out of the top 10 markets by rent growth -- San Francisco, San Jose, Boston, Austin, Seattle, and Denver -- are technology-oriented markets.

In turn, sales have followed. For example, in San Francisco, the number of sales rose 21 percent in the first half of 2012, according to Real Capital Analytics. Deal volume was up by 75 percent. The number of deals in Austin rose 31 percent. The value of the deals increased 48 percent.

In New York's tech-heavy Midtown South, which has the lowest U.S. vacancy rate, sales in the second quarter rose by 43 percent, while those Midtown, the traditional office market, fell 53 percent according to Cushman & Wakefield.

Still, there could be plenty of interest in owning well-leased buildings, where yields are higher compared with bonds. Eastdil Securities is poised to start marketing Worldwide Plaza, a 47-story 2 million square-foot Manhattan office building occupying an entire Midtown block between Eighth and Ninth avenues.

According to preliminary marketing material obtained by Reuters, the building is 90 percent leased. It will become the North American headquarters for Nomura Holdings Inc (8604.T), who will occupy 820,000 square feet of space. The building also is the global headquarters of law firm Cravath, Swaine & Moore LLP, whose lease expires in 2024.

The building is expected to attract foreign and domestic buyers looking for a bond-like investment.

(Editing by Ryan Woo)

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