Some of the nation's largest mortgage companies are stepping up foreclosures on delinquent homeowners. That will likely lead to more Americans losing their homes just as the Obama administration's housing-rescue plan gets into gear.J.P. Morgan Chase & Co., Wells Fargo & Co., Fannie Mae and Freddie Mac all say they have increased foreclosure activity in recent weeks. Those companies say they have lifted internal moratoriums which temporarily halted foreclosures.