A major flood insurance bill was a rarity when it passed what is widely derided as a do-nothing Congress in 2012, but a year and a half later, there is now an enthusiastic bipartisan effort to gut it.

This week the Senate is expected to approve a measure that would block, repeal or delay many of the key provisions of the Biggert-Waters Flood Insurance Reform Act, which was sponsored by Representative Judy Biggert, an Illinois Republican, and Representative Maxine Waters, a California Democrat.

Tucked into broader transportation legislation, the bill had enthusiastic support across the political spectrum, from liberal environmentalists to fiscal conservatives.

But Ms. Waters is now leading an effort in the House to gut the legislation she sponsored. And this week, the Senate is expected to pass a measure that would stymie the law, an effort that has support from across the political spectrum, from prominent liberals like Senator Elizabeth Warren, Democrat of Massachusetts, to conservatives like Senator Marco Rubio, Republican of Florida.