It began as a "very heartwarming gift," in President Reagan's words, from one head of state to another. But there are fears that West German Chancellor Helmut Schmidt's recent present of two bald eagles to the president and First Lady has brought new peril to the already endangered national bird.

The eagles, named Carol and Captain, were to be shipped here in time for an August celebration marking the eagle's 200th year as America's national emblem. But administration officials became concerned about possibly violating the 1940 Bald and Golden Eagle Protection Act, which makes it a crime to kill the national bird, and also forbids importing or exporting it.

Then the Interior Department, which enforces the eagle act, came to the rescue with a legal opinion that appears to clear the way for the eaglets to enter the United States.

The problem, according to several environmental lawyers, is that it also shoots some holes in the laws designed to protect the national bird from extinction. Two environmental groups obtained copies of the June 30 opinion yesterday and released them, along with loud denunciations.

Interior Department spokesmen did not answer repeated queries yesterday about the opinion.

The ruling by Solicitor William H. Coldiron does not mention the German eaglets, but environmentalists suggested that it was prompted by the Carol-and-Captain problem. Coldiron ruled that the eagle act's prohibitions do not apply to the federal government--a reinterpretation that apparently covers gifts to presidents.

But the opinion also weakens regulations that protect the birds from threats on federal land, said attorney Michael J. Bean, author of "The Evolution of National Wildlife Law."

Bean said the it could wipe out a ban on timber-cutting near bald eagle nests in national forests in five states. He said it also could undo a similar ban on mining federal coal in such areas.