Federal regulators are moving quickly to broker a deal for Washington Mutual as the savings-and-loan comes under mounting financial pressure, according to people briefed on the talks.

Even as Washington moves to bail out financial institutions, the fortunes of Washington Mutual have spiraled downward. On Wednesday, Standard & Poor’s, a major credit rating agency, downgraded Washington Mutual’s debt further into junk territory, citing the increased chance that the company might have to be split up to facilitate a sale.

Washington Mutual insists that it is well-capitalized and has adequate access to funding and noted “the rating actions do not affect the safety of customer deposits, which are insured up to the limits allowed” by the federal government.

Brad Russell, a Washington Mutual spokesman, declined to comment on speculation about a possible sale. Still, shares fell 94 cents, or 29 percent, to $2.26 a share on Wednesday, leaving them down 83 percent this year.