UPDATE 1-Vanguard replaces AllianceBernstein on two funds
* Names others to manage most of $3.7 bln U.S. Growth fund
* "What took Vanguard so long?" - Vanguard analyst
* Vanguard says it replaced AllianceBernstein on 2nd fund (Adds details on another fund replacement, and on funds AllianceBernstein still manages)
BOSTON, Oct 7 (Reuters) - Vanguard Group Inc said on Thursday it replaced AllianceBernstein Holding LP (AB.N) as manager of most of its $3.7 billion Vanguard U.S. Growth Fund (VWUSX.O) and on a smaller second fund after long stretches of subpar performance.
Vanguard, the privately held giant Pennsylvania fund firm, said it named Wellington Management Co and Delaware Investments to replace AllianceBernstein, which had run about two-thirds of U.S. Growth and had served as an adviser to the fund since 2001.
The remaining one-third of the fund will continue to be run by William Blair & Co, Vanguard said. "We are confident that the new advisers ... will help the U.S. Growth Fund regain some of its past luster," said Vanguard Chief Executive Bill McNabb in a statement.
U.S. Growth's record has been a sore spot for Vanguard for some time. Though a sometime standout, its returns rank it just average or worse over three-year and five-year periods, according to Morningstar Inc.
"One has to ask what took Vanguard so long?" Daniel Wiener, who writes a newsletter for Vanguard investors, said in a note. Wiener also asked whether Vanguard would drop AllianceBernstein from an annuity growth portfolio it also sub-advises, which he called "another disaster story."
A Vanguard spokeswoman confirmed it had replaced AllianceBernstein on the second fund, the Vanguard Variable Insurance Fund - Growth Portfolio, with about $235 million in assets. Management of most of it was turned over to Wellington and Delaware.
U.S. Growth's largest holdings as of June 30 included computer makers Apple Inc (AAPL.O) and Hewlett-Packard Co (HPQ.N), and search firm Google Inc (GOOG.O), according to Morningstar.
An AllianceBernstein spokesman declined to comment on whether the moves would affect the company's earnings. The company had $467 billion under management as of August.
It continues to run parts of other Vanguard funds including the Windsor (VWNDX.O), International Value (VTRIX.O), and Global Equity (VHGEX.O) funds -- overseeing about $6 billion in all, according to Vanguard.
"We remain deeply committed to our valued relationship with Vanguard," AllianceBernstein said in a statement. "We continue to provide several investment services to the firm and will work to further enhance our partnership with them."
Shares of AllianceBernstein were up 16 cents to $27.15 in late morning trading. (Reporting by Ross Kerber, editing by Dave Zimmerman and Gerald E. McCormick)