This image, provided by PBS, shows co-anchors Judy Woodruff, left, and Gwen Ifill in the newsroom of "PBS Newshour." Ifill and Woodruff are the first women to co-anchor a national daily news program on television. (Robert Severi/AP)

National TV newscasts have tried just about every kind of anchor configuration over the past six decades: A lone male anchor. A lone female. Two men. A man and a woman. Even three men.

But two women? Perish the thought. No national evening broadcast has ever dared put a pair of women on air together to read the news each day. Apparently, as a character in the 2004 satire of 1970s culture “Anchorman: The Legend of Ron Burgundy” put it: “It’s anchorman, not anchorlady! And that is a scientific fact.”

Until now.

Starting with its broadcast Monday evening, the “PBS Newshour” will feature two women in the anchor chairs. The venerable program — anchored for years by founding fathers Robert MacNeil and Jim Lehrer and lately by a series of rotating anchors — will be co-anchored by Judy Woodruff and Gwen Ifill.

The new era at “Newshour” will start out with a big “get”: Ifill will interview President Obama on Monday as part of his round robin of media interviews to build support for a U.S. military strike against Syria. The interview will air Monday night. (“Newshour’s” co-producer, WETA, channel 26, carries the program at 7 p.m. in Washington.)

Woodruff and Ifill have anchored “Newshour” before, alone or in combination with each other (they handled the political conventions and election night last year together). Still, their installation as regular co-anchors is a small cultural milestone for American TV news.

Such a pairing is “a no-brainer,” given the duo’s experience and familiarity to “Newshour” viewers, Woodruff says. “If you have two people on your team who really click, what difference does it really make” if they happen to be women?

Nevertheless, Woodruff, 66, acknowledges the symbolic import of the moment. Coming in with the first wave of female TV reporters and anchors in the early 1970s, she recalls looking for her first job and being brushed off by news directors with some variation of “We don’t believe a woman’s voice is authoritative.”

Ifill, 57, a former Washington Post and New York Times reporter, was a later arrival to TV, starting with NBC News in the mid-1990s and moving to public television as host of PBS’ “Washington Week” in 1999. She notes the “first” of her partnership with Woodruff, but plays down its significance. “We’re moving on the assumption that people want to see us, and the woman thing doesn’t help or hurt,” she said. Viewers “know us, and know what they’re getting.”

Following the all-male, Huntley-Brinkley era of TV news, women were first paired with men on local newscasts in the 1970s to create contrast, notes Bob Papper, a former news director and Hofstra University professor who has studied newsroom demographics for almost 20 years. The notion was that the two genders balanced each other, with a woman’s “softer” style providing contrast to the man’s harder edge.

Not incidentally, the boy-girl approach (as well as its mixed-race variation) was thought to appeal to the widest possible audience, thus boosting ratings, says Papper.

While a female-female set up is increasingly common at local stations across the country, Papper points out that it’s still unusual during the two most-viewed local newscasts, typically at 6 and 11 p.m. At those hours, the male-female pair rules. Papper says this may reflect the audience; women are the predominant part of the news audience during most hours, but there’s more gender balance among viewers at 6 and 11 p.m.

On the other hand, Papper doesn’t discount the effect of sexism and hidebound thinking among the people who run TV stations. He recalls working as an assistant news director at a station in Ohio about 20 years ago when the radical notion of having two women anchoring the news came up. Senior managers promptly shot the idea down.

“The reaction was, ‘My God, that would be different.’ And heaven forbid we should do something different.” Even today, he says, “A lot of it is that [TV stations] are risk averse. We’re not talking about cutting-edge people here.”

The most famous him-and-her combo on network news — Dan Rather and Connie Chung on CBS — was a notable disaster. The lack of chemistry, even tension, between Chung and Rather doomed the anchor team to a run of just 23 months between 1993 and 1995. Rather took back the solo gig at the end.

The Rather-Chung fiasco may have taught the networks a lesson. Since that time, the three leading broadcast networks (ABC, CBS and NBC) have used solo anchors on their evening newscasts. Cable news networks, with 24 hours of airtime to fill each day, have experimented with different anchor formats, but none has ever used two women, according to two veteran cable-news producers.

Focus-group research into anchor combinations indicates that viewers look for “a balance of power” among anchor teams, says Craig Allen, an associate professor at the Walter Cronkite School of Journalism at Arizona State University. This balance, he notes, has been most easy to achieve with a male-female combination, mimicking the traditional mom-dad/boy-girl dynamic.

The dynamics of a single-gender team may be a little trickier. Although it’s not clear in all studies, Allen says there’s some indication that viewers respond best when one member of a female-female anchor team “leads” — that is, is substantially more visible and popular than the other.

The “junior” anchor is “a newcomer who complements the major-domo figure,” he says. This unequal relationship “tends to wash out the perception of gender altogether. Had two average anchors been teamed, gender probably would have been noticed and affected the [audience’s] perception,” he said.

Allen doesn’t expect a lot of fireworks from Woodruff and Ifill — they’ll “co-exist,” much as McNeill and Lehrer did all those decades before them, he said — but “PBS viewers [will] enjoy having them there as individuals.”

Ifill has her own take on the subject. Asked why it took so long for two women to attain the most visible spots on a news broadcast, she replied: “Because men rule the world. I’ve never worked at a place where the people who rose didn’t look like the people in power.” Now, she says, “we’ve slogged away for so long, it just seemed to make sense.”