FACTBOX: Role of U.S. Congress in Fannie-Freddie support

(Reuters) - Congress needs to authorize the package of measures announced Sunday by the U.S. Treasury and Federal Reserve to support mortgage finance giants Fannie Mae and Freddie Mac

The companies own or guarantee nearly half the U.S. mortgage market and have become vital to its functioning at a time when home values are slumping and defaults are rising.

Key lawmakers have expressed support for adding the measures to a housing bill already being considered by the U.S. Senate and House of Representatives that includes creating a new regulator for Fannie and Freddie.

The major elements to be added to the bill would be:

* A temporary increase in a government line of credit available to either company, by an amount to be determined by the Treasury. Each company can currently draw up to $2.25 billion.

* Authority for the Treasury to purchase equity in either of the companies if necessary. (The Treasury has declined to detail how such an investment might work except to say the terms would include condition to protect the taxpayer)

* A "consultative role" for the Fed in setting capital requirements and financial safety and soundness standards for the two companies.

(Reporting by Tim Dobbyn and Kevin Drawbaugh; Editing by Leslie Adler)