The Democratic House, which handed President Reagan his head two weeks ago, is preparing to say uncle on Nicaragua.

Unnerved, apparently by their defiance -- and success -- in turning down any form of aid to the "contras" fighting the Sandinista government of Nicaragua, the Democrats are frantically stitching up amendments, modifications and compromises that will prove that they are "responsible" -- that is, still scared to death of Reagan.

House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) who threw his entire and considerable bulk into the fight against a Republican proposal to give nonlethal help to the contras, explained the switch. It's all the fault of Daniel Ortega, the prickly, green president of Nicaragua, who went to Moscow two days after the House vote.

"He's embarrassed us, to be perfectly frank," O'Neill said Tuesday.

The speaker did not point out that he himself had gone to Moscow last month and had spent almost four hours with Mikhail Gorbachev, without loss of sumptuous offices or his official limousine. But Ortega, whose failure to cotton to the ways of democracy so infuriates Reagan, has yet to learn that freedom to travel, while it is enshrined in our law, is a sometime thing where he is concerned.

On the more embarrassing circumstance of showing the Democrats as the party that puts embarrassment above principle, O'Neill had nothing to say. The Democrats have been desperately trying to find themselves a new identity. Their imminent capitulation to a policy that a majority of the country and the western world find immoral, illegal and unattractive suggests that they have decided to be the party with the movable convictions, the petty party that judges a man -- at least Ortega -- by his travels.

Some Democrats wanly declared, after Reagan wiped them out in the MX missile vote, that it was the high point of his presidency, to be followed by decline. But here they go again, fleeing desperately from the awful onus of saying no to him on something that matters.

A reversal on contra aid would be the first test of Reagan's post-Bitburg strength and would reassure the president that a noxious itinerary is not necessarily fatal to someone who runs a large country.

The Republican gloating has already, understandably, begun.

It was led by Reagan, who progressed from Germany's angst to Spain's turmoil. "I think that there are some people having second thoughts and discovering they have been the victims of a disinformation campaign."

Said his pollster, Richard B. Wirthlin, "Sometimes Ronald Reagan wins even when he loses."

The Democratic leadership is resigned to the inevitable. The speaker reiterates his opposition to giving any kind of aid and comfort to the terrorists who remind Reagan of our Founding Fathers, but he says the game is up. His candor is taken by some of his flock as a license to stray.

Majority Leader James C. Wright Jr. (D-Tex.) held out hope that maybe the Democrats at least could keep the money from going to the contras through the CIA.

Deputy Majority Whip William V. (Bill) Alexander Jr. (D-Ark.) said, "Democrats opposed to Reagan's war are less than a majority -- others are from regions who want a John Wayne foreign policy." Although he comes from Arkansas, Alexander is staunchly against the contras. "They are mercenaries, bought and paid for by Reagan. They are known as Reaganistas in the region, and we owe them nothing."

But the Democrats are on their way to underwriting Reagan's fantasy that a dilapidated little country with an unhousebroken government constitutes a clear and present danger to the world's mightiest democracy.

Actually, for some members, who know better, Ortega's untimely call on Moscow was a welcome alibi. Ortega's indiscretion, without so much as a tip of the hat to Democrats who had pleaded for a reciprocal gesture, gives them cover to do what they want to do, which is to stand tall with the president against "communist tyranny." Moderate and conservative Democrats profess to feeling "betrayed" by the liberals who prevailed on them to support humanitarian aid to the contras to be administered through international agencies and then, on final passage, voted to end all involvement in the affairs of Nicaragua.

They suffer no embarrassment at the prospect of a new vote that means more war, more suffering, more hardships and more atrocities for the plain people of Nicaragua.

The Democrats used to call themselves the party that cares. Now it seems, they would just as soon be seen as the party that caves. It's safer, they think.