Fed tapering will be for wrong reason: El-Erian

A tapering of the Federal Reserve's $85-billion-a-month bond-buying program this year is "almost a given," but there won't be enough economic growth to justify the reduction, Pimco's Mohamed El-Erian told CNBC on Thursday.

Wall Street expectations have been focusing on a start as soon as September, a month that Pimco's CEO and co-CIO called critical not only because of the Fed but German elections as well.

In a "Squawk Box" interview, El-Erian said the economic numbers don't justify a slowdown in bond purchases known as quantitative easing, but Fed Chairman Ben Bernanke may do it because of his concerns about the risks of continuing the program.

(Read more: Steady Fed: Printing presses to keep on rolling)

"The reason they'd be doing it is because they're starting to get more and more worried about what Mr. Bernanke has called 'the cost and risk of prolonged unconventional and experimental monetary policy,'" El-Erian said.

He added the Fed is going to continue to try to shift market attention from QE to central bank plans to leave short-term interest rates near-zero for the foreseeable future. "Then they're going to enhance the forward guidance to support that pivot from QE to the rate."

In the statement Wednesday after Fed's two-day meeting, policymakers said rates won't increase anytime soon, and QE will continue every month while the economy continues to improve at a "modest" pace. The Fed provided no further clues on any taper timing.

Stock investors are "hearing the two things they want to hear, which is gradual economic improvement and central banks in 'business as usual' mode," El-Erian said. "And the markets are getting support from ... this notion that we may get this handoff down the road from assisted growth to genuine growth."

"We're not seeing it yet in the economic data," he continued, "but the hope the Fed has is the longer it waits, the better the data will become. That is a hope as opposed to a very high probability."

On Wednesday, the government reported second quarter economic growth of 1.7 percent—nearly double expectations. But a downward revision for the first quarter, to 1.1 percent from 1.8 percent, put a damper on some of the hope of a 2 percent to 3 percent growth rate in the second half of the year.

(Read more: Slow growth aside, jobs data could mean better second half)

"The equity market has priced in a lot of good news," El-Erian said, but he warned that all the optimism "is not fully supported by the economic fundamentals." He added, "We'd be more cautious at this stage on risk assets."

By CNBC's Matthew J. Belvedere. Follow him on Twitter @Matt_SquawkCNBC.