Hedge fund manager William Ackman laid out a plan on Tuesday to restructure mortgage finance companies Fannie Mae and Freddie Mac as more investors expressed doubts about the government's proposal to prop up the battered institutions.

Ackman, who runs New York based hedge fund Pershing Square Capital and is known for betting big against bond insurers, said his plan would effectively recapitalize the two companies, leaving them with a healthier mix of equity and debt.