As predictably as spring rains comes the seasonal controversy over water between President Carter and Congress.

The usual slugfest over "pork barrel" projects is on the agenda again, as was evident by the grilling of Secretary Cecil D. Andrus before a Senate Appropriations subcommittee Wednesday. North Dakota's senators took stron exception to Andrus' recent characterization of the Garrison diversion project as "a dog," Andrus made no apologies.

But the debate this year is likely to be more sophisticated and complex than ever before -- although, perhaps, equally nasty. Last year, the president vetoed the water projects appropriations bill, and a compromise was worked out that appeared to please no one.

This year, Carter officials want to change the rules that govern water project selection. While the administration's water policy proposals released in June are considered timid by environmentalists, the dispensers of congressional largess view them as a direct threat.

"It's going to be party hard to sell," confided one Interior Department official.

On the other hand, a Senate coummittee staffer said, "there aren't the pressures of an election year this time and everyone's watching government spending."

The outcome will after how the federal government spend millions of dollars for dams, irrigation and flood-control projects. Three proposed water policy changes will be debated this year:

Carter has incorporated full funding of each new water project in the 1980 budget even though each may take years to complete. The unspoken assumption is it would be harder for Congress to approve new projects when they have to pay for them all at once. Congressional committees oppose the idea, fearing they will lose control over the pace of construction.

Carter wants to beef up the Water Resources Council, an independent body made up of representatives of federal ag encies, to write new rules for future projects and make sure they are followed. The Army Corps of Engineers and the Bureau of Reclamation have been accused of exaggerating benefits and minimizing costs to please congressional sponsors. Those sponsors, for their part, were ready to abolish the council last year and are wary of any interference in their relationship with water agencies.

Carter will propose legislation soon to require states to pay 5 or 10 percent of the up-front costs of new projects. Traditionally, projects have been funded entirely by the federal government which is theoretically, paid back by farmers, power users and other beneficiaries. If the states foot part of the bill, "they'll take a closer look" at which projects are really needed, Andrus said.

While the debate over water policy proposals will be lively -- if somewhat murky and technical to outsiders -- it will affect only projects being authorized in the future. What to do about projects that have been approved by Congress under the old rules, and are now considered 'boondoggies," is an even more controversial question.

On Garrison Diversion, a $600 million irrigation project that is vehemently opposed by environmentalists and by the Canadian government, Andrus proposes a compromise: reduce the projects's size from 225,000 acres to 93,000 acres. That won't satisfy critics who say it will still pollute rivers, endanger wildlife and waste productive farmland. Nor will it please proponents who say it will not increase agricultural production or provide as many jobs as the full project.

Sen. Quentin Burdick (D-N.D) predicted Andrus' plan will fail, but Sen. Milton R. Young (R-N.D.) indicated he might be receptive to some kind of compromise if Andrus promises not to condemn any farmland for the project.

The biggest battle may be over the massive Tennessee- Tombigbee waterway, targeted by environmentalists as the project to kill this year. The administration is lying low for feart of antagonizing powerful southern senators, including John Stennis (D-Miss.), who support the $1.6 billion project.

However, a court suit brought by railroads and environmentalists has revealed serious flaws in the Corps of Engineers' economic justification fo the waterway. Sen. Gaylord Nelson (D-Wis.) is introducing a bill to halt it, although it is 20 percent complete.

Environmentalists are upset about Carter's overall water projects budget, which reflects a 16.5 percent increase for fiscial year 1980 -- much of it because of the inclusion of full funding for 26 proposed new water projects costing a total of $578 million. "The stringent analysis and waste-elimination which were applied to most other parts of the Carter budget are conspicuously absent in the water area," the National Wildlife Federation concluded.

However Andus said the increase reflects "the administration's support for sound water resources development" -- a support viewed with skepticism by Congress. "It emphasizes," Andrus said, "that we are not opposed to good water projects, although we remain adamantly opposed to bad water projects."

The distinction will be what the fight is all about.