Share prices at most Washington area companies jumped during the first half of this year, but local firms say they are not necessarily taking advantage of the gains to add jobs or buy new equipment just yet.

Instead, many are watching how the economy fares the next six months before making any big bets.

An analysis of 139 publicly traded companies in the region showed stock prices grew an average of 16.58 percent between December 31 and June 28, according to data from Bloomberg. By comparison, the S&P 500 gained 12.63 percent in that time.

The rise reflects a national trend. Investors, searching for higher returns than they might get from real estate or bonds, have piled into stocks, buoyed by the Federal Reserve’s move to pump money into the economy through bond buying.

The surge has put smiles in the C-suite, but many executives are aware that investors could bail if the Fed begins to turn off the spigot. The market’s big dip last week reinforced the point, as investors sold off shares on mixed fears the economy is strengthening, even if consumer spending at some retailers is not. A stronger economy could mean the Fed could scale back its activities.

Find out how stocks fared by industry.

“It’s no secret that nationally we’re in a moment of incredible uncertainty,” said Lawrence R. Creatura, portfolio manager at Federated Investors. “Whether you’re an individual or a corporation, you’re being careful about spending and investing.”

Area companies are taking note. Instead of funneling new-found market value toward investments and new ventures as they might have during past market booms, many said they are waiting on the sidelines for the stock market to stabilize.

At Sandy Spring Bank, where shares rose 11.33 percent during the first half of the year, executives say they can afford to be patient.

“It’s really about what [the rising stock price] will give us down the road,” said Philip Mantua, chief financial officer of the Olney-based bank. “It gives us flexibility and a strong currency if we decide to [make] an acquisition in the future.”

Investors aren’t the only people buying

While they wait for the economy to pick up, area firms say they are also increasingly using extra cash to buy back shares of their own stock.

Northrop Grumman, the Falls Church-based defense contractor, announced a $4 billion stock repurchase in May. That same month, Neustar said it would buy back $250 million in shares, and the Advisory Board Co. announced it would repurchase an additional $100 million in shares.

Other large companies, including Marriott International, Capital One Financial and Verisign, have said they plan to repurchase up to $1 billion in shares. At General Dynamics, executives say much of the company’s $3.76 billion in readily available cash will go toward stock buybacks and dividend payouts to stockholders.

“We expect to deploy almost all, if not all, of our free cash flow to share repurchase and dividends,” Phebe N. Novakovic, the company’s chief executive and chairwoman said in July. “We’ll continue to use our free cash flow in shareholder friendly ways, and maintain that strong balance sheet to give us flexibility.”

Nationwide, companies bought back $412 billion in stocks during the first half of this year — a 61 percent increase from a year ago, when repurchases totaled $256 billion, according to stock market research firm Birinyi Associates.

Those stock buybacks have an added benefit for some company executives: They help lift share prices even higher by reducing the number of shares in the market, ultimately leading to heftier pay packages for many at the top.

Executive pay days

The majority of executives now receive more than half of their pay in equity, whether in the form of company stock options or performance-based awards, said Aaron Boyd, director of governance research for Equilar, an executive compensation research firm.

“A change in a company’s stock price certainly has a large impact on the executive’s overall pay package,” he said. “As the markets have improved, overall pay for executives has also been climbing.”

Some companies, though, are finding ways to cash in on rising stock prices.

At District-based Vanda Pharmaceuticals, executives capitalized on the rallying stock market with a secondary public offering two weeks ago. The company sold 4.68 million shares, raising approximately $48.3 million.

Eventually, Vanda says it plans to use those funds — along with another $100 million in cash reserves — to market its new drug, a treatment for a rare sleep disorder, that is currently awaiting FDA approval. The medication isn’t scheduled to hit shelves until next year, but chief executive Mihael H. Polymeropoulos said it made sense to offer new shares while the stock market was faring well.

“Of course you should raise money when you can,” Polymeropoulos said. “We did so at a time when market sentiment was favorable on Wall Street.”