WASHINGTON — An upstate New York Republican is slated Tuesday to shatter the congressional record of former Brooklyn Democratic Rep. Elizabeth Holtzman as the youngest woman ever elected to Congress.

Elise Stefanik, 30, is favored to win in New York’s upstate 21st District and make history as the youngest female to win a seat in the House. Holtzman was sworn in at age 31 in 1973 at a time when women weren’t even allowed in the congressional gym.

“I’m just sorry it’s a not a Democrat,” Holtzman told The Post. “But hats off to her. We need more young women in Congress.”

Holtzman, who co-founded the first women’s caucus, never expected her record to last more than 40 years and would check with Congress every election to see if any young woman had finally surpassed it.

Stefanik, a Harvard graduate and a former aide to President George W. Bush, was not the person she had in mind.

“I think more important than gender, it’s what people stand for,” said Holtzman, a lawyer in Manhattan.

Stefanik has touted her youth and fresh ideas on the campaign trail in the race against 50-year-old Democrat Aaron Woolf, a documentary filmmaker who owns a Brooklyn organic eatery. She feels honored “to have added an additional crack in the glass ceiling.”

She commended Holtzman’s achievement and pledged to encourage more young women to run. “I hope my record is broken faster than hers,” Stefanik told The Post.

Women represent just 18.5 percent of the seats in Congress and this Election Day isn’t expected to do much to ease the gender gap. But several female candidates are poised to make history.

In Utah, Mia Love is strongly favored to become the first African-American Republican woman elected to Congress.

In New Jersey, Democrat Bonnie Watson Coleman is on her way to becoming the first African-American woman to represent the Garden State in Congress.

The biggest prize could go to Iowa Republican Joni Ernst, who has momentum in the critical race that could determine control of the Senate. She’d become the first woman ever elected to Congress in Iowa and the first female combat veteran in the Senate, having served in Kuwait as a company commander in 2003 and 2004.

Debbie Walsh, director of the Center for American Women and Politics at Rutgers University, said that while it’s important to acknowledge these breakthroughs, “it would be a mistake” to lose sight of the bottom-line under-representation of women in Congress.

“There’s still a lot of work to be done,” Walsh told The Post.