WHEN ABC announced its new fall line-up this week, the network was intriguingly silent about two things:

*Who will replace Hugh Downs as Barbara Walters’partner on the original, Friday-night edition of “20/20”?

*And will the pairing of Walters and Diane Sawyer be kept next year when “20/20” moves to Thursday night?

“It’s not like we’ve made a decision and we’re keeping it from people,” said ABC News spokeswoman, Eileen Murphy.

“We have a different night, one anchor who is leaving the broadcast and we just see it as an opportunity to try some different things. We’re not going to rush into any decisions,” Murphy said.

Downs’ departure from the series opens up the seat next to Walters, automatically creating the most prominent job opening in TV news.

It is possible ABC will move in one of its already-established hosts – Connie Chung or Charlie Gibson, for instance, who currently anchor the Monday night version.

The network will also have to consider offering the open seat to anchorman Peter Jennings – asking him to do double duty like CBS anchor Dan Rather, who hosts newsmagazine “48 Hours” and is a correspondent on “60 Minutes II.”

“I don’t feel like I’m leaving ABC in a lurch,” Hugh Downs told The Post yesterday. “They’ve got a lot of good anchors. Charlie Gibson might be willing to do another one of these ’20/20s’ since Diane and Barbara are doing two.

“I think there are other people who have great anchor ability too,” Downs speculated, “like Tom Jarriel.”

The behind-the-scenes intrigue appears to be already underway.

As well, ABC says no decision has been made about keeping Walters and Sawyer as an anchor team.

Both Walters and Sawyer are said to be good friends, but fiercely competitive with each other.

They also boast the highest salaries in network news – each reportedly under contract for around $10 million a year.

Neither Walters nor Sawyer would be pleased if the other was given an extra night, insiders said.

ABC officials will also have to take into account is the heavy schedule both women have outside of the show.

Sawyer and Charlie Gibson will continue as interim hosts of “Good Morning America” through next year, the network says.

“They are having so much fun, they’ve agreed to stay on while we groom the next generation of anchors for ‘GMA,'” said David Westin, ABC News president.

Meanwhile, Walters continues to appear on “The View,” which she also produces, at least three times a week.