Executives at companies making everything from electrical components and power systems to automotive parts say the fiscal stalemate is prompting them to pull back now, rather than wait for a possible resolution to the deadlock on Capitol Hill. Democrats and Republicans are far apart on how to extend the Bush-era tax breaks beyond January — the same month automatic spending reductions are set to take effect — unless there is a deal to trim the deficit. The combination of tax increases and spending cuts is creating an economic threat called “the fiscal cliff” by Ben S. Bernanke, chairman of the Federal Reserve. Until recently, the loudest warnings about the economy have come from policy makers and economists, along with military industry executives who rely heavily on the Pentagon’s largess and who would be hurt by the government reductions. But more diversified companies like Hubbell Inc. in Shelton, Conn., have begun to hunker down as well. Hubbell, a maker of electrical products, has canceled several million dollars’ worth of equipment orders and delayed long-planned factory upgrades in the last few months, said Timothy H. Powers, the company’s chief executive. It has also held off hiring workers for about 100 positions that would otherwise have been filled, he said. “The fiscal cliff is the primary driver of uncertainty, and a person in my position is going to make a decision to postpone hiring and investments,” Mr. Powers said. “We can see it in our order patterns, and customers are delaying. We don’t have to get to the edge of the cliff before the damage is done.” The worries come amid broader fears that the economy is losing momentum — the annual rate of economic growth in the second quarter fell to 1.5 percent from 2 percent in the first quarter, and 4.1 percent in the last quarter of 2011. On Thursday, the Commerce Department reported that factory orders unexpectedly fell 0.5 percent in June from the previous month, while data on the labor market released Friday showed job creation still falling short of the level needed to bring down the unemployment rate. All told, the political gridlock in the United States, along with the continuing debt crisis in Europe, will shave about half a percentage point off growth in the second half of the year, estimates Vincent Reinhart, chief United States economist at Morgan Stanley. More than 40 percent of companies surveyed by Morgan Stanley in July cited the fiscal cliff as a major reason for their spending restraint, Mr. Reinhart said. He expects that portion to rise when the poll is repeated this month. “Economists generally overstate the effects of uncertainty on spending, but in this case it does seem to be significant,” he added. “It’s at the macro- and microeconomic levels.” Unless Congress acts to extend the tax provisions and comes up with a budget deal that averts the planned reductions in military spending and other government programs, taxes will rise by $399 billion while federal government spending will fall by more than $100 billion, according to an analysis by the Congressional Budget Office. The end-of-year battle comes after Democrats and Republicans have failed over the last year to reach long-term agreements on how to tackle the budget deficit. Last week, Congressional leaders did manage to agree tentatively to keep the government financed through next March, extending a deadline that had been set to expire Oct. 1, but that deal did not address the extension of the tax cuts or spending reductions. All together, the fiscal cliff’s total impact equals slightly more than $600 billion, or 4 percent of gross domestic product, and if no action is taken, the Congressional Budget Office projects the economy will shrink by 1.3 percent in the first half of 2013 as a result. With many Fortune 500 companies now setting budgets and planning for 2013, chief executives say they cannot afford to hope for the best. Wall Street is also paying more attention: over the last few weeks, chief executives of companies like Honeywell, U.P.S. and Eaton all cited the uncertainty as a threat to earnings in the second half of 2012.