GREENSBORO — Profit gains earned through job cuts and factory closings in the absence of a global economic recovery are starting to reach their limit.

Third-quarter profits and sales for the Standard & Poor’s 500 Index probably fell in unison for the first time in three years, according to analysts’ estimates compiled by Bloomberg. Per-share earnings may have dropped 1.7 percent on average after they were little changed in the second quarter. Sales may have slipped 0.6 percent, the data show.

While most companies plan to keep a lid on spending, lower expenses aren’t leading to the same kinds of increases they reported earlier this year. Hewlett-Packard Co., the world’s largest personal-computer maker, already forecast full-year profit that trailed analysts’ estimates, FedEx Corp. cut its annual earnings forecast, and Intel Corp. projected lower third- quarter sales, with all three citing softening demand.

“A lot of the earnings growth that we’ve seen has been related to cost reductions,” said Peter Jankovskis, co-chief investment officer for Oakbrook Investments in Lisle, Ill., which manages more than $3 billion. “Now many of those cost-reduction efforts have run their course. Without revenue growth, there is no room for profit to expand further.”

Alcoa Inc., the largest U.S. aluminum maker, kicks off the third-quarter earnings season Tuesday and is projected by analysts to report a 13 percent drop in sales, the biggest drop in three years, on plunging prices for the commodity. That may wipe out per-share earnings, according to estimates.

The earnings season “may be rather ugly,” based on early reports so far, according to Gina Martin Adams, a New York-based strategist at Wells Fargo & Co.

“While recession in the U.S. is not necessarily imminent, earnings are weakening fairly quickly,” Adams wrote Monday in a note. For the fourth quarter, companies may struggle to match analysts’ estimates as data indicates U.S. growth is stabilizing at a “depressed” pace, she said.

The U.S. economic slowdown, coupled with a worsening environment abroad, is leading more companies to consider further job and spending cuts. A Business Roundtable survey last month showed 34 percent of U.S. chief executive officers anticipate they will have fewer domestic employees in the next six months. That’s up from 20 percent when the survey was conducted last quarter.

The gloomier outlook reflects “global demand flattening out, particularly in Europe and China,” Jim McNerney, CEO of Boeing and Business Roundtable chairman, said on a Sept. 26 conference call.

CEOs in the survey also projected U.S. gross domestic product will expand 1.9 percent this year, down from a projection for 2.1 percent growth three months ago.

In one sign of economic improvement, the U.S. jobless rate unexpectedly fell in September to 7.8 percent, the lowest since President Barack Obama took office in January 2009. The S&P 500 is also on course for its best annual performance since 2009 after gaining 16 percent so far this year.

Sources of uncertainty

Companies may use third-quarter conference calls to trim profit forecasts for the rest of the year, according to Tobias Levkovich, an equity strategist at Citigroup in New York. Uncertainty over the presidential election and automatic deficit cuts that could go into effect starting in January may contribute to a lack of management confidence, he said.

U.S. companies dependent on overseas revenue were probably among the hardest hit in the third quarter. General Motors, the world’s largest automaker, may report adjusted per-share earnings tumbled 42 percent with falling demand and price cuts in Europe trimming revenue 1.9 percent to $36 billion.

The euro area’s economic slump is deepening, with at least five of the region’s 17 nations already in recession. Last month, economic confidence unexpectedly dropped, service industries shrank and a gauge of manufacturing by Markit Economics showed contraction in that sector as well.

“Europe is a very significant weight on revenue” for U.S. companies, said Mark Zandi, chief economist at Moody’s Analytics in West Chester, Pa. “The fallout from the European debt crisis is starting to hit sales and profitability more broadly.”