The number of American homeowners that could be foreclosed upon rose by 24 percent in the first quarter of the year, but experts warn that figure could rise higher if the Obama administration’s plan is not adopted by lenders. Almost 804,000 homeowners were sent a foreclosure-related notice between January and March, up from about 650,000 in the first quarter of 2008. Obama’s plan aims to assist 9 million borrowers to refinance or modify their loans to avoid foreclosure, but it has been unclear if banks will participate in the program. US Housing Secretary Shaun Donovan said he expected the number of foreclosures to increase, especially among speculative, vacation and vacant homes. He said foreclosures could start declining in the summer.