At times in last year's campaign, Jimmy Carter came on like a true-believing Hubert Humphrey Democrat on economic questions. If elected, he would pump up the economy; drive down unemployment; rewrite the tax laws to help the little man; overhaul the welfare system and raise the federal share of welfare costs; lead the United States toward national health insurance.

And you could depend on it.

But there were also occasions last year when a different Jimmy Carter appeared, sounding almost word for word like his opponent, Gerald Ford. If elected, he would balance the federal budget before the end of his first term: would defer welfare reform and health insurance and other new spending programs if he had to, to achieve a balanced budget: and in any case would not let government spending grow any faster than the economy as a whole, so that taxes would not rise as a percentage of income.

Now it begins to seem as if this second less well advertised Jimmy Carter was the real one.

Jody Powell, Carter's press secretary, insists that "last summer and fall we . . . tried to tell you he is a fiscal conservative." But that is not how many Democrats remember it.

Some, including the party's leaders in Congress, think the President may be deserting them on the economy - and led by Speaker Thomas P. (Tip) O'Neill (Mass.) they told him so in no uncertain terms in a blunt-spoken session last Tuesday at the White House.

Republicans, meanwhile, are gleeful at the Democrats' discomfiture. If the President switches sides on economic issues, "he'll be welcome," House Minority Leader John J. Rhodes (Ariz.) told reporters half in jest and whole in earnest as the week wore on.

Rep. Augustus F. Hawkins (D-Calif.), a senior member of the Congressional Black Caucus, describes Carter's policies caustically as "slightly more conservative than Richard Nixon's."

Carter's Tuesday meeting with O'Neill and the other Democratic leaders was the second in two days. On Monday Carter stunned his audience by saying his No. 1 objective is a balanced budget by fiscal 1981 the spending year that will begin Oct. 1, 1980.

The Democratic elders said little Monday, but at the second session O'Neill told the President, according to one member of Congress who was present:

"You should not assume our silence meant consent. This is the Democratic Party and we have traditionally been concerned with people who are out of work and we have a moral commitment to those people that no one else speaks for."

It is not merely these meetings with Carter that have the Democrats somewhat concerned, however.

Item: Ford last January proposed that the government run a $57.2 billion deficit in the current fiscal year. Carter, now that he has withdrawn his proposed $50-a-head tax rebate to pep up the economy, is suggesting a significantly smaller $48.7 billion deficit. Yet this retrenchment comes with unemployment still at 7 per cent: there are 6.7 million would-be workers unemployed.

Item: Carter ast week announced that he will not send Congress a detailed welfare reform proposal until August: that his plan will not take full effect until 1981: and that, initially at least, it will involve no increase in federal expenditures. National health insurance seems to have been shoved even farther into the future. Carter's determination to have that balanced budget in fiscal 1981 is one of the reasons given for these stretch-outs.

Item: Carter said in the campaign that he would cut defense spending $5 billion, freeing more money for domestic uses. That pledge, too, has lost some clarity since Election Day. Two weeks ago Carter resisted a cut the House Budget Committee proposed in defense spending for the coming fiscal year, as part of the budget resolution finally approved. Carter's resistance to the defense cut helped throw the entire budget resolution off the track. It was defeated its first time up in the House, and has to be rescued by the leadership.

There are other complaints. Carter promised tax reform time and again in the campaign and reform proposals will be sent to Congress later this year, his aides say. In the meantime, he proposed an important cut for low-income taxpayers as part of his tax bill to stimulate the economy, on which Congress will complete action this week. But he also has proposed a tax cut for independent oil producers, which is part of that same bill, and which undoes one section of the Tax Reform Act Congress passed in 1976. Talk of tax reform, moreover, has given way in the last several months to talk of tax "incentives" to encourage increased business investment and expansion, and that shift has not been lost on Carter-watchers.

Carter has also resisted as large a minimum-wage increase as the AFL-CIO and some of its Democratic supporters in Congress would like. The labor federation has little good to say about Carter these days. AFL-CIO President George Meany was asked at a press conference last week if there was anything labor liked about the administration so far. Meany answered in one syllable: "No."

Members of Congress are more circumspect when asked similar questions.

The Senate's assistant majority leader, Alan Cranston (Calif.), was one of those who, alongside O'Neill on Tuesday, pressed Carter not to neglect unemployment and other domestic needs for a balanced budget's sake. But having had his say with the President, Cranston was noting for public consumption at week's end that a balanced budget was not Carter's only goal, that the administration is also shooting for a 4.3 per cent unemployment rate and 4 per cent inflation rate by 1981. Thus another Carter objective is "a job for every family," Cranston said.

In the Nixon and Ford years, the White House and the Democratic Congress often were at loggerheads, with Congress sending legislation to the President's desk only to see it killed by veto. Carter's election was supposed to mean the end of this divided government. Now some members, particularly in the House, say they can imagine divided government continuing - a Democratic Congress that wants to spend more pitted against a Democratic President who does not. But most members are less alarmist at this early stage.

Sen. Gary Hart (Colo.) says it is true that "some" of his fellow Democrats think Carter has been too conservative. "But not a lot" think that, Hart adds.

Hubert Humphrey (Minn.) recalls Carter "a man of fiscal restraint, perhaps more than the traditional liberal Democrat would like," and says he is not sure Carter can hit his balanced-budet target no matter how hard he tries.

But these remarks are tame: it is hard to find anything but such polite observations in the mannered Senate, and many Democratic senators are entirely comfortable with Carter's stands so far. "He's simply being realistic," says Dale Bumpers (Ark.).

On the House side there is more of a bite to the commentary. Charles Rangel (N.Y.) is one example. "He is not talking about balancing the budget when it comes to defense increases," this Black Caucus member says. "It bothers me where his priorities are coming from."

Adds Fortney H. (Pete) Stark (Calif.): "One of these days it's going to dawn on him he needs the liberals."

From the Republican side, John Anderson (Ill.), a member of the GOP leadership, says Carter has "really boxed himself in by saying he's going to balance the budget. As surely as night follows day that means he's going to have to put the clamps on his brethren on the Democratic side."

But Barber Conable (N.Y.), ranking Republican on the House Ways and Means Committee, says it is not polities that have boxed Carter in, but basic economies.

Unemployment is high. Conable agrees - but so is the inflation rate. Wholesale prices have risen at an annual rate of 13.1 per cent in the last three months. And Carter has to fear inflation just as Ford did, in Conable's opinion.

"He's under the same constraints in acting that Gerald Ford would be if he were President." Conable told a reporter. Pretty soon, "he'll have to apply the brakes just like Ford."