WASHINGTON (AP) _ The government is requiring the two biggest housing finance companies, Fannie Mae and Freddie Mac, to finance more mortgages for low- and moderate-income families, boosting their total to $2.4 trillion in such mortgages over 10 years.

The action, announced today by HUD Secretary Andrew Cuomo, means the companies must buy an additional $488.3 billion in mortgages from banks and other lenders, enough to provide housing loans for some 7 million families of modest means.

The Department of Housing and Urban Development, which regulates Fannie Mae and Freddie Mac, has raised the proportion of mortgage loans they must earmark for low- and moderate-income families from the current 42 percent of their total purchases to 50 percent.

Under the plan, the first increase will be to 48 percent next year.

``This action will transform the lives of millions of families across our country by giving them new opportunities to buy homes,'' Cuomo said.

Despite the booming economy, he said, affordable housing ``is in a crisis stage in this nation.''

``There are still real needs out there. ... There's plenty of work for us to do.''

Fannie Mae and Freddie Mac are government-chartered corporations whose stock is publicly traded. They buy mortgages from original lenders such as banks and package them into securities for resale to investors.

Fannie Mae agreed to the new 50 percent level for low- and moderate-income mortgages after intense negotiations with HUD officials, Cuomo and other agency officials said. Freddie Mac, however, is still in discussions with the agency, which could impose the requirement unilaterally if it wished.

Cuomo said his department preferred to cooperate and negotiate with the two companies.