A year ago, it seemed unthinkable for any network to even consider programming aggressively against ABC on Sunday nights. “Desperate Housewives” was peaking, “Grey’s Anatomy” was gaining, and “Extreme Makeover: Home Edition” was beating even Fox’s “Simpsons” among adults 18-49.

When the other networks announced their schedules last spring, they put on virtually nothing to challenge ABC on the night.

What a difference a year makes.

With “Housewives” on the decline since January and “Grey’s” moving to Thursdays come fall, suddenly ABC seems vulnerable, and three of the other four networks are mounting very aggressive new challenges on the night.

It’s entirely possible that ABC will lose its edge. At the very least, the edge will become much duller.

With NBC’s “Sunday Night Football,” CBS’s “Without a Trace” and the CW’s urban sitcom block all moving to the night, Sunday will be competitive for the first time in two years.

“Moving ‘Without a Trace’ to Sunday night has the most potential of any programming move this season. It is the highest night for TV usage levels, and CBS used to rule that night until ABC bolstered it in recent years. Clearly CBS wants it back,” says one media researcher.

The other networks have chosen their counter-programming carefully, picking shows they believe will appeal to audiences that are somewhat different than “Housewives” viewers. The CW is courting black viewers, NBC is going after men, and CBS is wooing the older end of the 18-49 set.

All of those groups are watching ABC’s Sunday lineup but not in the sort of numbers they did last year.

“Housewives” has been fading since midseason. Sunday’s season finale posted its best 18-49 average since February, a 9.9, but that was down 26 percent from last year’s season finale, at a 13.4.

Meanwhile, “Home Edition” has dipped from a 6.5 average last season to a 5.9 this year, a falloff of 9 percent. That decline has been even greater during sweeps. It will receive a steep challenge at 8 p.m., facing the CW’s “Girlfriends” and “The Game,” which has gotten good early buzz, as well as the first hour of NBC’s “SNF” and the relocated “Amazing Race” on CBS, which appeals to the same family demographic.

In all, Sunday night will have nine timeslot changes for returning shows, also including switches on Fox’s comedy block, and three new shows, including ABC’s “Brothers and Sisters.”

By comparison, last year there was just one new show, Fox’s “War at Home,” and no other siginificant timeslot switches.

It’s still possible ABC could regain the dominance it showed earlier this year on the night. “Brothers” has received good early buzz from media buyers, who say the presence of Calista Flockhart, in her first show since “Ally McBeal,” may draw viewers.

And “Housewives” was up quite a bit over recent weeks for its finale, which ended the unpopular storyline about Betty Applewhite and her mysterious children.

But more likely, Sundays will become a night where all of the networks are able to carve out a niche. It may have the five strongest schedules for any night of the week, with no one network looking particularly weak. It will certainly be more interesting than the past two years, when ABC often doubled its nearest competitor.

As a report from Magna Global about CBS’s new schedule concludes, “Moving its hit ‘Without a Trace’ over from Thursday carries some risk but is certainly a risk worth taking, particularly with both ‘Grey’s Anatomy’ and ‘Crossing Jordan’ vacating the hour.”