The Federal Reserve will likely announce plans to stimulate the U.S. economy via a third round of quantitative easing (QE), though such a move will have muted effects, Neel Kashkari, managing director and head of global equities at fund giant Pimco, told CNBC.

Under QE, the Fed buys assets like Treasury holdings or mortgage-backed securities from banks, pumping the economy full of liquidity to push down borrowing costs and encourage investing and hiring, sending stock prices rising in the process.

The Fed has rolled out two such rounds (QE1 and QE2) since the downturn, injecting $1.7 trillion into the economy in the first round and then $600 billion in the second round with freshly printed money.

Editor's Note: Economist Unapologetically Calls Out Bernanke, Obama for Mishandling Economy. See What They Did

Fed Chairman Ben Bernanke has said the U.S. central bank cannot rule out QE3 if the economy fails to show sustained improvement, particularly in the labor market, which remains weak.

“From our perspective we think QE3 is a virtual certainty, but we don’t think that more liquidity is going to lead to more long-term sustainable real economic growth,” Kashkari told CNBC.

“We think that it can push up the prices of financial assets and make the headlines look better, but ultimately we have structural challenges facing our economy, and that’s going to require fiscal authorities to act. There is only so much Bernanke can do.”

Fed officials themselves have said Congress and the White House must take steps to pay down debts and narrow deficits, while at the end of this year, Bush-era tax cuts and other tax breaks expire at the same time automatic cuts to government spending kick in, a combination known as a fiscal cliff that could send the country back into recession if left unchecked by lawmakers.

Still, with fiscal reforms unlikely to take place in an election year, expect the Federal Reserve to act.

“I think the markets have priced in basically expecting that QE will be there. When flooding liquidity into the system, the money has to go somewhere and it ends up pushing up the prices of these liquid assets.”

Some Federal Reserve board members have said that if QE3 comes, policymakers shouldn’t announce a fixed amount of assets to be purchased as was the case in the first two rounds, opting instead to announce open-ended intervention.

Should that come, expect a stronger rally in equities markets.

“That could exceed the market’s expectations and you could see the markets rally from here,” Kashkari said.

Still, no matter what Bernanke announces, don’t expect any rallies to last, as monetary stimulus measures don’t make structural improvements to the economy.

“It’s not going to lead to long-term sustainable economic growth. It’s not going to bring our unemployment rate back down to 6 percent or lower. That’s going to require Congress and the executive branch.

“In many ways Bernanke is trying to treat the symptoms. It’s better to treat the symptoms than to do nothing, but I think he knows that he doesn’t have the tools necessary to treat the underlying disease.”

Other experts agree that QE carries diminishing returns.

While past easing measures have steered the country away from deflationary collapse and may have halted the advance of rising unemployment rates, more intervention would likely produce little benefits while further applying inflationary pressures down the road.

“Nobody likes it when the punch bowl is taken away, but the party has gone on too long,” said Doug Cote, chief market strategist at ING Investment Management, according to CNNMoney.

“It’s time to get back to a normal economic recovery.”

The Fed will hold its next two-day monetary policy meeting Sept. 12 and 13.

A CNNMoney survey of investment strategists finds that 93 percent said they don’t think the Federal Reserve should announce more stimulus at its next meeting, while 77 percent of economists surveyed agreed.

Editor's Note: Economist Unapologetically Calls Out Bernanke, Obama for Mishandling Economy. See What They Did