The Sacramento is the state's biggest river and a vital supplier of fresh water to San Francisco Bay, part of the largest estuary on the West Coast of the Americas.
Brown and other project supporters say the tunnel project would modernize California's current, outdated north-south delivery system, where pumps and overall water withdrawals are blamed for the steady dwindling of native fish and other wildlife that depend on delta water. Brown's father, then-Gov. Pat Brown, oversaw building of that water project in the 1950s and 1960s.
The revised state proposal talks of building the tunnels in stages, with one of the four-story-high tunnels built now, and another at some unspecified time. The new proposal also would cut the number of intakes pulling water from the Sacramento River, from three to two.
Water contractors have previously talked of the possibility of permanently paring the project from two tunnels to one, in hopes of more easily winning support for a smaller project. The newly posted revised state proposal marks the first time the state has publicly put such a proposal in writing, and asked builders vying for any tunnel project to plan specifically for a one-tunnel option.
The state did not immediately release a revised cost for the scaled-down proposal.
Osha Meserve, an attorney working for Northern California farmers opposing the project, said the revised proposal makes "more clear the project they want to do is a failure. Now they're trying to morph into something else."
Asked for comment Tuesday, state water officials said they were preparing a response.
Project opponent Restore the Delta said any one-tunnel project would require new environmental studies and applications.
Bob Muir, a spokesman for Southern California's giant Metropolitan Water District, the project's main backer along with the Brown administration, referred questions to the state and to an association of state water contractors.
Water districts choosing to buy into the project would manage the design and build of the tunnels, including choices on contractors, rather than the state's Department of Water Resources.