It being Christmas, the lame-duck session of Congress gave some thought to the poor. But they had this fear of a presidential veto, you see, and they had to get home for Christmas, so the $50 million both houses had voted for the destitute and the homeless sank without a trace.

Nobody knows exactly why.

Some people said that since the $50 million was in the jobs bill, which President Reagan vowed to veto, it was doomed. Others said that Congress had second thoughts about giving money directly to United Way, with its bureaucracy and its overhead, even though United Way officials assured interested members that, with the help of major charities, they could get help to the needy within 45 days and would cut administrative costs to 2 percent.

Everyone agrees that the purse for the poor could have been put in another part of the bill. Reagan never said he would veto soup kitchens and emergency shelters at a time when 12 million Americans are out of work. Usually funds that are agreed upon by both House and Senate sail through conference. But the $50 million disappeared late Sunday night, a victim of negligence, fatigue and the pressure to go home.

"I looked down and the ground was gone," was the explanation given by Sen. Mark O. Hatfield (R-Ore.), chairman of the Senate Appropriations Committee.

Rep. Silvio O. Conte (R-Mass.) said the conference had gone on for 12 hours, and he was briefly out in the hall arguing with a senator about something else. By the time he got back, the $50 million had vanished.

On Monday afternoon, Sen. David H. Pryor (D-Ark.) rose to register his objection to ignoring the unfortunate, the people who live in cars and depend on soup lines and church basements for their daily bread.

"We are giving $11.5 billion for foreign aid. We are giving a salary increase to the members of the House, but somehow we are not really answering the needs, especially in this Christmas period, of those who do not have a home and those who literally have nothing to eat," Pryor said morosely.

Sen. William Proxmire, (D-Wis.), who had been at the conference where they forgot the poor, said, "We faced that great big monster of a veto."

Sen. Donald W. Riegle Jr.(D-Mich.) dis-tressed Hatfield by suggesting that the $50 million had been a hostage to the House pay raise. The Senate virtuously refused the extra cash, but assured itself a much heftier take by lifting the lid on its lecture fees.

If the members had braved Reagan's supposed wrath, the pay raise would have gone back to the floor. To vote for it once was valiant; twice would have been suicidal. Besides, their first duty was to keep the government going.

"Frankly," said Pryor from the depths of the lame-duck pits, "I think if the government continued to run, it might be worthwhile. But I wonder if the Senate ought to continue to run."

If the lame-duck session had been a horse, the Humane Society would have had it shot. If it had been a child, it would have been sent to summer camp by popular subscription. Reagan perpetrated it on the grounds that urgent action was required on Social Security, which never came up.

Members, who knew it might look a little funny that they had raised their own wages while so many had none, rationalized that they had not been heartless.

They had, after all, increased fuel assistance to the needy. They could starve in comfort -- assuming, of course, that in this time of foreclosures and evictions they have a roof over their heads. That's lame-duck compassion for you.

The president leads the way in giving lip service to charity. He acts like he thinks it is something that others do. At the national Christmas tree lighting, he had a characteristically cheery thought:

"How about those of us who are employed making sure that those of us who are not will nevertheless have a Merry Christmas?"

There was no next sentence that began, "and as an example, Nancy and I have invited to the White House to enjoy Christmas with us the family of a steelworker who lost his job three years ago."

Or did he say he was sending a check to the Salvation Army, which, as Mark Shields remarked in his morning radio commentary, without benefit of Madison Avenue public relations consultants, "has become the most widely admired institution in this country"? The answer is no.

In Washington, at both ends of Pennsylvania Avenue, they talk about the poor and then forget them. Next year, they all say, will be better -- more jobs, more help. Let them eat promises for Christmas.