WASHINGTON — Charles T. Manatt, a former Democratic National Committee chairman and ambassador during the Clinton administration, died Saturday at age 75, his law firm said.

Manatt was party chairman from 1981-85, the first term of Republican Ronald Reagan and a difficult period for Democrats. A longtime California Democrat, Manatt was credited with building the party’s finances, modernizing it through computerization, direct mail and other initiatives, and building a new headquarters in Washington.

On the eve of the 1984 Democratic convention in San Francisco, presidential nominee-in-waiting Walter Mondale tried to replace Manatt with Carter administration official Bert Lance. Mondale backed off after an outcry in the party, triggered in part by Manatt’s positive reputation in the ranks and Lance’s ties to a banking scandal for which he had been tried and acquitted.

Reagan cruised to an easy victory over Mondale for a second term.

Manatt and the party fared better in 1992, when he was co-chairman of Bill Clinton’s presidential campaign. Clinton later appointed Manatt as ambassador to the Dominican Republic, where he served from 1999-2001.