Not every domestic agency would have its budget cut next year by President Reagan. Spending for the Interior Department's Bureau of Reclamation, which builds dams and irrigation systems in 17 western states, would increase by 23 percent, more than even the Defense Department.

Environmental groups, which oppose many of the bureau's water projects as wasteful and destructive, are predictably upset. "Total hypocrisy," Brent Blackwelder of the Environmental Policy Center here, says of the water budget. "It is totally at odds with Reagan's effort to cut back domestic spending."

Other aspects of the administration's water policy are less offensive to the environmentalists; some are even reminiscent of the "reforms" in water policy that President Carter unsuccessfully proposed early in his term.

The budget contains only planning money for future projects and no construction funds for new starts. However, to appease westerners who have an ever-expanding wish list, the budget message notes that $43 million will be requested for new projects later in the year, once the administration has decided how to make states and localities share the costs. An important tenet of Carter water policy was that the states and private parties that benefit from projects should help pay their costs, on grounds that this would save money and, perhaps more important, save water.

The administration also supports changes in the 1902 Reclamation Act that would force western growers to pay more for the federal irrigation water they use, and favors new fees that would require waterway users to bear more of the cost of those projects.

But these aspects of administration policy do not make up in environmentalists' eyes for the decision to press ahead with those projects the Bureau of Reclamation and Corps of Engineers already have under way. Many of these projects are large and controversial. A number of them were on the famous "hit list" of projects that Carter tried and failed to stop early in his term. The likely future projects are minor by comparison.

In the fiscal 1983 budget, Reagan has asked Congress for $3.82 billion for water development. He continues full funding for projects such as the $2 billion Tennessee-Tombigbee waterway, which environmentalists and fiscal conservatives in Congress came close to stopping last year.

Over environmentalists' objections, the Reagan budget would also fund such other controversial undertakings as the O'Neill and North Loop projects in Nebraska, the Garrison Diversion in North Dakota and the Narrows Dam in Colorado that Carter had tried to kill.

The Bureau of Reclamation would spend $950 million, up nearly a fourth over fiscal 1982. The budget of the Army Corps of Engineers, which also builds dams and navigation projects, would decrease by 6 percent, to $2.7 billion, but an administration source said the reduction is mostly due to the normal winding down of several large projects.

Eastern and midwestern members of Congress point out that their states would receive only $8 per capita for water development, while the South and West would get $26. "The administration's budget reflects priorities that work against the interests of older industrial states," according to a statement by Reps. Robert W. Edgar (D-Pa.) and Carl D. Pursell (R-Mich.) for the Northeast-Midwest Congressional Coalition.

"No money is available to repair urban water systems . . . . But the budget leaves funding for massive water supply projects in America's arid states virtually intact . . . . The federal government cannot and must not abandon the North's massive investment in its economic life-support systems, only to build new systems at greater cost in the South and West."

From the point of view of some westerners, however, the administration is not doing enough to build new projects. At a hearing of the Senate energy subcommittee on water resources some days ago, an impressive array of politicians testified in favor of particular projects. Sen. Larry Pressler (R-S.D.) wanted Congress to authorize a $70 million pipeline to pump Missouri River water to 51 towns and a $42 million expansion of the Belle Fourche reservoir to be used by energy companies that have yet to request the water.

It was a measure, however, of the changed temper of the times, that a project pushed by Wyoming Gov. Ed Herschler, a $106 million enlargement of the Buffalo Bill Dam, includes a commitment by the state to pay $42 million in up-front construction costs. "We're not attempting to rip off the East in pork-barrel politics," Herschler said.

At a House appropriations subcommittee this week, officials from the Corps of Engineers came under sharp questioning from members of Congress hostile to the administration's cost-sharing and user-fee proposals. Rep. Tom Bevill (D-Ala.), citing a cement plant in Mobile that could be hurt by a $100 million cut in the corps' dredging budget, said Congress would increase the dredging funds without enacting user fees to pay for it. Although a corps official said cost-sharing negotiations are under way over improvements in the ports of Baltimore and Hampton Roads, Rep. Jamie Whitten (D-Miss.), the chairman of the Appropriations Committee, said such requirements could delay water development by four or five years.