May 20 (Bloomberg) -- SLM Corp., the biggest U.S. education lender, climbed the most in more than two weeks in New York trading on speculation that terms of an industry rescue plan will be favorable for the company.

President George W. Bush signed a law May 7 letting the Education Department buy loans that private lenders have been unable to sell to investors amid credit tightening triggered by subprime mortgages. The department may disclose details of the program today in Washington, said Kevin Bruns, the executive director of America's Student Loan Providers, a trade group.

``It's been a volatile stock because investors are trying to speculate about which way the Department of Education is going to lean,'' said Sameer Gokhale, an analyst at Keefe Bruyette & Woods Inc. in New York.

SLM, known as Sallie Mae, rose $1.02, or 5.2 percent, to $20.78, at 4 p.m. in New York Stock Exchange composite trading. That was the biggest percentage gain since 8.9 percent on May 2, after Congress gave its final approval to the legislation.

The Education Department's press office in Washington didn't respond to a request for comment.

Sallie Mae said in an e-mail it will provide ``critical information'' in a conference call tomorrow about the federal guaranteed-loan program. The Chronicle of Higher Education reported today that Sallie Mae may announce it's withdrawing from that program if the new terms don't enable the company to make money. The paper didn't name the source of the information.

``It's certainly a possibility that Sallie Mae is bluffing, but lenders are leaving the business because of this,'' said Gokhale.

Shares of Reston, Virginia-based Sallie Mae had fallen 64 percent in the 12 months through yesterday.

Market Share

Sallie Mae accounted for 28 percent of the federally guaranteed student-loan market in 2007. Other lenders had a combined 51 percent share, and the federal government's Direct Loan Program provided 21 percent, according to Lehman Brothers Holdings Inc.

Mark Kantrowitz, publisher of FinAid.org, a Web Site about student loans, said Sallie Mae pulled out of an investor conference call so it could instead accommodate the call with colleges.

If Sallie Mae does leave the market, the effect on students and their families may not be known for a month, Kantrowitz said.

``Students would have problems finding a lender, or they might find a lender but that lender might pull out,'' Kantrowitz said. ``It certainly is going to be inconvenient for families.''

To contact the reporter on this story: Oliver Staley New York at ostaley@bloomberg.net.

Last Updated: May 20, 2008 16:20 EDT