WASHINGTON (Dow Jones) - Mortgage giants Fannie Mae and Freddie Mac could be getting a new regulator thanks to a bill offered Friday by Senate Banking Committee Chairman Richard Shelby .

The bill offered by Shelby, R-Ala., allows the regulator to adjust the companies' assets and set capital standards, controversial powers that not all lawmakers will be comfortable with.

Fannie (FNM) and Freddie (FRE) hold about $1.5 trillion worth of mortgages and related securities, almost one-fifth of U.S. residential mortgage debt outstanding.

Federal Reserve Chairman Alan Greenspan told Shelby's panel Thursday the investment portfolios don't do much to lower U.S. mortgage rates. And, he said, the holdings actually pose a risk to the U.S. economy.

"Because it is a highly leveraged operation and one which requires very sophisticated hedging of interest rate risk, it's imparting a significant potential systemic risk to the American financial system," Greenspan told senators.

A hearing about the bill, one of several House and Senate attempts to tighten oversight on the mortgage firms, is set for Thursday morning.

A version passed by the House Financial Services Committee earlier in the year didn't include limits on the portfolio holdings.

Shelby's bill, which also requires the companies to obtain regulatory approval to offer new products, is closer to what the Bush administration is seeking for the two companies. Both Fannie and Freddie have weathered massive accounting scandals, drawing heightened congressional scrutiny.

The House bill, offered by Rep. Richard Baker, R-La., also creates a new regulator. A controversial provision also directs both Fannie and Freddie to set aside some of their after-tax profits to assist affordable housing programs.

Created by Congress, both Fannie and Freddie buy mortgages from lenders and bundle them into securities to sell to investors.

Shares of McLean, Va.-based Freddie Mac gained 12 cents to close at $65.65 Friday, while Washington, DC-headquartered Fannie Mae ended the day at $58.40 , down 12 cents.

(END) Dow Jones Newswires

07-22-05 1713ET Copyright (c) 2005 Dow Jones & Company, Inc. Copyright (C) 2005 Dow Jones & Company, Inc. All Rights Reserved.