It's no secret that the Federal Reserve's program of pumping liquidity into the system has been fueling stock market gains like steroids goose baseball statistics. The Fed's most recent $600 billion program of bond-buying was dubbed QE2 (for quantitative easing 2).

But the question that has been looming recently is this: Since Fed Chairman Ben Bernanke has said that he will terminate the QE2 program in mid-June, what will become of the bull market that saw the S&P 500 nearly double from its 2009 lows? Is the party going to end or is the market healthy enough to continue to rise on its own steam?

A number of investment strategists say that caution is in order.

Kate Warne, investment strategist at St. Louis-based Edward Jones, says that this shift to a less supportive Fed will not lead to a broad market downturn, but it could have an impact on risk assessment. "The riskier stocks that have done the best over the last two years won't be the best performers going forward," she says. "We think equities will still do better [than fixed income], but portfolios may have become riskier than people realize. So they may want to rebalance into more defensive sectors," she says.

Specifically, she says, advisors may want to suggest moving their clients away from riskier stocks and into more defensive positions, like health care, consumer staples and utilities, which have underperformed in the bull market to date.

But the big-picture view? "We don't think that the end of QE2 will be a big disruption for the equities markets. We see it as a first small step toward a more normal Fed policy, which will be followed by a slow rise in interest rates," says Warne.

Jeremy Grantham, a strategist at the money management firm GMO, is more downbeat. The S&P 500, currently trading above 1,300, could indeed reach 1,500 by October, he says. But prudent investors won't hang around to find out while hoping to get lucky. Grantham recommends a "hard-nosed approach," which he describes as "having substantial cash reserves and a base of high-quality blue chips and emerging-market equities."

To be sure, we're already seeing the market trying to digest the looming end of QE2, says Prudential Financial's market strategist Quincy Krosby. "That, and the tightening globally, plus the rise of the dollar versus the euro, has the market getting more and more defensive," she adds. Krosby says that the best strategy at this point for financial advisors, given the uncertainty about the impact of an end of QE2, is to "have a more diverse portfolio, with more cash." She says investors should be "hedged to the downside," with a portfolio that makes no big bets, and that will "benefit from any scenario."

Christian Hviid, an independent investment consultant, notes that the end of QE2 has been "well telegraphed" by the Fed, so he doesn't expect any big surprises as the program of bond-buying ends in June. But he notes that reports of a slowing U.S. economy are troubling. Hviid says he expects to see the earnings per share of companies follow GDP downward, and suggests that advisors should be urging their clients to "de-risk" their portfolios. "If people want to remain invested in the equities markets, they should shift to lower beta stocks and dividend stocks," he says. "Raising cash to 2% to 6% might also make sense, as a safeguard."

While some strategists see the end of QE2 as a non-event, and some see it as a sign of an economy getting back to normal, most say they are more cautious.

"We weren't even supposed to have QE2, remember," says David Rosenberg, chief market strategist for Gluskin Sheff & Associates, a high-net-worth money management firm based in Toronto. "But after the Fed ended QE1, we had a big drop in the S&P, and eventually Uncle Ben [Bernanke] cried uncle and instituted QE2," Rosenberg says. Arguing that "nothing's really changed" and that "we're still in the middle of a recovery from a balance sheet depression of historical proportions," Rosenberg suggests advisors "do what worked in the period between QE1 and QE2, which means taking beta off the table and concentrating the equity part of clients' portfolios on earnings visibility, strong balance sheets and defensive sectors, like consumer staples."