The phone call from the constituent was succinct - and undeniably clear. The increase Congress voted in Social Security payroll taxes last December was more than taxpayers could stand, and President Carter's tax cut wouldn't make up for it, no matter what the White House said. Then came the tag-line: "Rich people don't have enough votes to get you re-elected, but working people do."

The congressman on the other end, Rep. Jim Mattox (D-Tex.), lost no time in responding.Not only did Mattox draft a reply, he also introduced a bill to head off the payroll tax rise now scheduled for next January. "There's a lot of sentiment back home about payroll taxes," Mattox says, clearly concerned. "And we'd better do something or some of us may not be back."

Mattox isn't the only lawmaker who now thinks Congress made a mistake last year when it approved legislation increasing the payroll tax. Dozens of other senators and representatives are running scared over the issue - from panic-stricken freshmen to nervous old veterans. And most of them voted for the tax-hike bill last December.

Indeed, voter protests over the coming payroll tax increases have been mounting so rapidly in recent days that it now seems an odds-on bet that Congress will move to head them off more quickly than expected. Although only a few weeks ago any such legislation seemed a year or more away, momentum has been growing for action this year - certainly before the November election.

The evidence has been cropping up all over Capitol Hill. Two weeks ago, the House Ways and Means Committee was snagged for two days debating whether to roll back last January's rise. The proposal - a largely symbolic measure in the panel's annual budget recommendations - lost by only 1 vote. And last week, House Budge Committee members showed strong support for a rollback.

A key test vote may come Wednesday, when, at the demand of 92 congressmen, the issue is scheduled to come up at a meeting of the House Democratic Caucus. If the caucus votes formally to seek rollback legislation, House leaders effectively will be forced to go along with the effort. If that happens, observers predict, the Senate won't be far behind.

The major problem is how to go about undoing December's payroll tax vote. By far the easiest way would be simply to roll payroll tax rates back to their 1976 levels and make up the difference by earmarking some of the money that otherwise would have gone to the president's tax-cut package. Then, when the issue comes up again two years from now, Congress would take another look.

But the lawmakers have other plans to choose from as well. One, backed by liberal Democrats and Republicans, would separate the Medicare and disability insurance programs from Social Security and finance them with income tax revenues rather than with the payroll tax. Another, by Rep. James A. Burke (D-Mass.), would use income tax revenues for one-third of the present program.

There also have been suggestions that the lawmakers enact a simple tax credit that effectively rebates the payroll tax increase without actually cutting into the Social Security trust fund. But the support for a rollback is indisputable: The Burke bill alone has 140 co-sponsors in the House and less-ambitious rival measures have 40 to 50 co-sponsors each.

The congressional turnabout is virtually an overnight development. As late as six weeks ago, Congress was still relatively satisfied with itself for having cleared the December hurdle. The issue last year was how to "save" the Social Security system from bankruptcy. Raising payroll taxes seemed a simple solution. Any major overhaul could wait until 1980.

Since then, however, the lawmakers have been hit with a spate of complaints by constituents, whose consciousness was awakened by a previously enacted payroll tax increase that went into effect Jan. 1.When the lawmakers went home for the Washington's Birthday recess, they were called on the carpet by angry taxpayers, and told to undo the tax.

The response has surprise even some supporters of the rollback effort. Rep. Abner J. Mikva (D-Ill.), a liberal Ways and Means Committee member who is sponsoring a bill of shift the Medicare program out of Social Security, had little hope of seeing his bill pass when he introduced it a month ago. But Mikva now says payroll tax relief is "almost a sure thing." Many agree.

Indeed, congressional and administration leaders still haven't adjusted to the change. Both Rep. Al Ullman (D-Ore.), chairman of the Ways and Means Committee, and Sen. Russell B. Long (D-La.), who heads the Senate Finance Committee, oppose any reconsideration of last year's tax increase this session. Officials fret the lawmakers may botch it again if they act in undue "haste."

The administration has been waffling over the issue. When the question first arose a few weeks ago, Secretary of the Treasury W. Michael Blumenthal said he'd go along with whatever Congress did. But other officials, including Charles L. Schultze, the president's chief economist, have seemed decidedly more reluctant.

Last week, Blumenthal, Labor Secretary Ray Marshall and Secretary of Health, Education and Welfare Joseph A. Califano met privately on the question, with Califano and Marshall leaning toward some accommodation. The very next day, though, Blumenthal abruptly toughened that stand, telling the House Budget Committee he "strongly" opposed any change before 1980.

Admittedly, the administration is caught in a somewhat ironic twist. It was Carter who first proposed splitting Medicare off last year to avoid a payroll tax rise, but Congress rejected the plan as too wild and irresponsible. Now that the public has gotten a taste of the tax-rise approach - and rejected it - Congress wants the administration's plan but Carter is holding back.

The administration's new-found conservatism, however, holds little attraction for the now-harried legislators. When Blumenthal broaches his you-had-your-chance-last-year approach at a Budget panel hearing last week, Texas' Mattox retorted testily: "Now that Congress has realized its mistake, it'd be nice if you'd help us set it straight."

Indeed, the pressures now appear to he so strong that congressional leaders have warned the White House privately it had better start drafting its own rollback recommendations before the efforts gets too far. As one key congressional figure put it, "It'd be better for them to get in early enough to influence the outcome than to have to fight the battle on the floor."

The question is in how to go about "correcting" last year's action. Burke's proposal to shift one-third of Social Security's financing to income tax revenues is too radical for conservatives and moderates, who want to preserve what they call the "insurance" character of the retirement fund. (Actually, that notion is a myth, but it's widely held by the public.)

The proposal to strip away Medicare and the disability insurance program from the retirement portion of Social Security - and finance them through income tax revenues - is less unpopular, but still presents some problems. Opponents fear it would open the way for congressional tinkering with eligibility and benefit requirements - which shouldn't be done in haste.

Congress was planning to take a look at this and other issues - such as whether to broaden the Social Security program by requiring government workers, now exempt from the payroll tax, to participate - but that was supposed to be a good year or two off. The consensus so far seems only that the payroll tax rise should be rolled back - not on how to repair the system for the long-run.

Some Hill experts say that seems most likely to emerge is the quick-fix solution: Simply freeze the payroll tax at its 1976 levels for the next two years and pay for it with monies from the president's tax-cut package.

The way the plan would work, Congress simply would trim Carter's income tax cut package to $19 billion from the $25 billion the president proposed, and use the remainder as a one-shot grant to pay for the part of the Social Security program the payroll tax rise would have financed. Then, sometime in 1979, Congress would reconsider the Social Security question for 1980.