WASHINGTON — Representative Alexandria Ocasio-Cortez on Friday endorsed an all-female slate of progressive candidates through her new political action committee, using her clout in the insurgent left and the considerable campaign funds she has drawn to counter the Democratic establishment in key races around the country.

The endorsements of the congressional candidates — including one who is challenging Senate Democrats’ preferred candidate in Texas — amount to a powerful stamp of approval for a diverse group of newcomers. They also are a clear sign that Ms. Ocasio-Cortez, a celebrity of the liberal left, intends to leverage her influence among activists to try to reshape the Democratic Party.

The move also underlines the struggle among Democrats that is defining the race for the presidency, which is pitting Senator Bernie Sanders, the self-described democratic socialist, against more moderate candidates who are presenting themselves as better able to appeal to a broad section of voters in taking on President Trump. Ms. Ocasio-Cortez has traversed the country to campaign for Mr. Sanders, and her efforts to pull Congress to the left parallel his bid to deploy his progressive message to emerge as the Democratic nominee, an effort that has instilled fear in many centrist lawmakers who believe it could cost them their seats.

“One of our primary goals is to reward political courage in Congress and also to help elect a progressive majority in the House of Representatives,” Ms. Ocasio-Cortez said in an interview. “There’s kind of a dual nature to this: One is opening the door to newcomers, and the other is to reward members of Congress that are exhibiting very large amounts of political courage.”