Towers Watson, a big benefits consulting firm, surveyed senior financial executives last year and found that two-thirds planned to decrease the stock portion of their companies’ pension funds by the end of 2010. They typically said their stock allocations would shrink by 10 percentage points.

“That’s 10 times the shift we might see in any given year,” said Carl Hess, head of Towers Watson’s investment consulting business. Economists have speculated that a truly seismic shift in pension investing away from stocks could be a drag on the market, but they say it would not be long-lasting.

Corporate America’s change of heart is notable all on its own, after decades of resistance to anything other than returns like those of the stock markets. But it’s even more startling when compared with governments’ continued loyalty to stocks. When governments scale back on the domestic stocks in their pension portfolios these days, it is often just to make way for more foreign stocks or private equities, which are not publicly traded.

Government pension plans cannot beef up their bonds that mature many, many years from now without dashing their business models. They use long-range estimates that presume high investment returns will cover most of the cost of the benefits they must pay. And that, they say, allows them to make smaller contributions along the way.

Most have been assuming their investments will pay 8 percent a year on average, over the long term. This is based on an assumption that stocks will pay 9.5 percent on average, and bonds will pay about 5.75 percent, in roughly a 60-40 mix.

(Corporate plans do their calculations differently, and for them, investment returns are a less important factor.)

The problem now is that bond rates have been low for years, and stocks have been prone to such wild swings that a 60-40 mixture of stocks and bonds is not paying 8 percent. Many public pension funds have been averaging a little more than 3 percent a year for the last decade, so they have fallen behind where their planning models say they should be.