Less than two years after he left Pacific Investment Management Company to run Harvard's $35 billion endowment, Mohamed El-Erian agreed to return to Pimco's offices in Newport Beach, California, the company said.

Pimco, famously guided by chief investment officer William H. Gross, said El-Erian would return in January 2008 as a managing director and as something new: He will also be co-chief investment officer alongside Gross and co-chief executive alongside current C.E.O. William S. Thompson.

The appointments appear to make El-Erian, 49, the heir apparent at Pimco, the consistently successful bond-fund-management firm owned by Allianz of Germany. But Thompson, 62, and Gross, 63, were quick to say they have no intention to surrender the reins in January.

"Neither Bill Gross nor I at this time have any plans to step down," Thompson said in a statement, noting that the firm's directors had just extended both their contracts for five more years.

Instead, Thompson suggested El-Erian will serve a kind of management apprenticeship, at least for now. "The demands and complexities of our current positions suggest that the addition of a unique talent such as Mohamed's will enhance both of our contributions going forward," Thompson said.

El-Erian has considerable management experience already. Before moving to Harvard to succeed Jack Meyer at the helm of the nation's largest college endowment, El-Erian ran Pimco's emerging-markets fixed-income team. He did very well.

His flagship fund, the Pimco Emerging Markets Bond Fund, posted an average annualized return of more than 19 percent when he was in charge. Before coming to Pimco in 1998, he had worked at Salomon Smith Barney and the International Monetary Fund.

He also excelled at Harvard. In his first full fiscal year there, the endowment had a return of 23 percent. But in July, the first month of the new fiscal year, Harvard lost about $350 million on investments in Sowood Capital Management.

Despite the loss in Sowood, a Boston hedge fund founded by a former Harvard investment adviser named Jeffrey Larson, the Harvard endowment still managed to end the month slightly in the black.

At the same time he was managing the endowment, El-Erian was also rebuilding the investment team at the Harvard Management Co., as the endowment is formally known.

When Meyer quit Harvard in 2005 to start the hedge fund Convexity Capital Management, he left with more than two dozen Harvard endowment staff members.

Finding a successor to Meyer was not easy. Harvard's endowment had racked up average annualized returns of 15.2 percent in the decade ending in June 2006, the Wall Street Journal reported. Endowments and foundations generally posted median annualized returns of 8.9 percent over the same period, according to Wilshire Trust Universe Comparison Service.

A Harvard spokesman told the Journal that the university does not have a successor in mind. "We're launching a search immediately," John Longbrake said.