By Matthew Goldstein and Jennifer Ablan

The year is not yet over and already the confessions are starting to roll in from some of the biggest U.S. money managers.

Bill Gross, manager of the world’s biggest bond fund, sent out a “mea culpa” letter late Friday to his many mom-and-pop investors, saying he’s sorry for putting up such bad numbers this year. Mea culpas from Pimco’s guiding light and the self-styled “bond king” are rare, largely because his Total Return Fund has long been one of the industry’s top performers.

But this year has been a tough one for Gross, who guessed wrong by betting heavily against U.S. Treasuries, which have turned out to be one of the biggest out-performers of 2011. The fixed income guru, who helps manage more than $1.2 trillion at Pimco, wasn’t farsighted enough to foresee a flight to Treasuries prompted by events like the European debt crisis, the battle over the U.S. debt ceiling and the general anemic state of the global economy.

Gross positioned his firm’s flagship fund for modest economic growth and that move left him putting up a “stinker,” as he says in his letter (hat tip to Dealbreaker.com). So, as things stand right now, the Pimco TRF fund with $242 billion in assets, is up only 1.06 percent year to date, compared to 3.99 percent gain for the benchmark BarCap U.S. Aggregate Index.

As we’ve reported, Gross now has repositioned his mammoth fund for zero economic growth. He’s levering up to buy longer-dated bonds with higher-yields and betting that a weak economy will keep interest rates low for a good long while. The way things are going that would seem to make sense. But as we know in the markets, timing is everything.