President Carter yesterday sent Congress a new message on the environment and acknowledged that his new energy program will "pose environmental risk" and require uncomfortable tradeoffs.

The president, in making the second major environmental message of his administration, didn't spell out any specific guidelines for the tradeoffs between energy and the environment.

But, he said, "I will work to ensure that environmental protections are built into the process of developing new technologies, and that when tradeoffs must be made, they will be made fairly, equitably, and in the light of informed public scrutiny."

In the heart of the message, Carter srongly reaffirmed his commitment to existing environmental laws and proposed a series of new initiatives to protect coastal areas, expand the nation's wild river program, and deal with acid water problems.

Specifically, Carter:

Declared 1980 the "Year of the Coast," a designation urged by conservationists, and proposed what he called a new coastal protection policy.

Asked Congress to declare four new wild and scenic river systems in Oregon, Idaho and Colorado, and directed that federal agencies protect other river systems under consideration for such designation.

Ordered the U.S. Forest Service to establish 145 new hiking trails by 1980.

Directed the Department of Interior to develop long range plans for recreation, energy exploration, and argicultural use in the 417 million acres of federal land it manages.

Declared a new transportation policy that stresses energy conservation

Established a 10-year program to study the threat of acid rain on the environment.

Carter also announced the appointment of Gus Speth as chairman of the Council of Environmental Quality. Speth, formerly a lawyer for environmental groups, has been a member of the council since March 1977. He succeeds Charles Warren who has resigned.

Much of Carter's long-awaited, 24-page special message appeared to be directed at reassuring environmentalists, who have expressed deep concern about the president's new energy program, that Carter is still interested in protecting the environment.

Particularly disturbing to environmentalists have been Carter's proposals for a crash program to develop synthetic fuels and to create an Energy Mobilization Board to speed up government decision making on new energy plants.

"What Carter has seemed to saying is, "I'm an environmentalist. But only when it's convenient," said Louise Dunlap of the Environmental Policy Center, a lobbying group.

Carter, in his written message, pledged that the board will be kept in check, and indicated that energy considerations would overrule environmental ones only in rare instances.

"We must not lose sight of the fact that, despite other pressures, the American people still care deeply about the quality of their environment," Speth said in a White House briefing. "They care about air pollution, trash and noise in their cities."

But the president's message left little doubt that energy is the administration's top priority. "There is no excuse for unnecessary red tape, which has plagued construction of some needed energy projects," Carter said at one point.

"Solving the nation's energy problem is essential to our economy and our security," he said at another. "We will not lose sight of out other goals, but we must not fail in ending the energy crisis."