The Federal Housing Finance Agency proposed new regulatory capital rules for Fannie Mae and Freddie Mac should they be released from federal conservatorship.

The regulator proposed a framework for risk-based capital requirement that "would use a series of approaches" instead of applying a flat percentage based on all mortgage assets regardless of differences in product features or terms. The two government-sponsored enterprises, or GSEs, would have to hold about $180.9 billion, or 3.2% of their portfolios, to meet the risk-based capital requirement based on their portfolios as of Sept. 30, 2017.

The FHFA also proposed two alternative rules for an updated minimum leverage capital requirement. Under those rules, the GSEs' minimum leverage capital requirement would range between $103 billion and $139.4 billion based on their portfolios as of Sept. 30, 2017.

The enterprises' capital requirements would remain suspended while they continue in conservatorship.

"It is appropriate to update its standards on enterprise capital requirements to provide transparency to all stakeholders about FHFA's supervisory view on this topic," the FHFA said.

The regulator is seeking comments on its proposed regulation.