Every year on this day, as Americans face their great annual hour of giving to the government, they complain that the federal income tax is soaking up more and more of their money.

This year they're probably wrong, although only barely so.

The federal tax bite as a whole is indeed rising. But the personal income tax is not nearly the villain that many taxpayers -- and politicians -- portray.

For culprits, look to the Social Security tax and the new domestic crude oil tax.

In terms of inflation-era dollars, the income tax, like everything else, is going up. But what is surprising is that, as a percentage of personal income, it has fluctuated within a relatively narrow range over the past decade, rising and then falling as Congress votes tax cuts to compensate for inflation's contribution to the federal treasury.

With the help of a tax cut voted two years ago, the federal income tax is expected to take 10.9 percent of total personal income for the 1979 tax year, according to preliminary Treasury Department projections. This is down slightly from the 11 percent estimate for the 1978 tax year. It is in the same ballpark as the 10.5 percent that was owed in 1970.

But don't breathe easier, figuring the worst is over. Without another tax cut, which Congress is striving to reconcile with its zeal for a balanced budget, the income tax bite -- sharpened by inflation -- would become precipitously bigger over the next few years.

As a sign of the current political mood, Congress will return from its Easter recess today whistling a tax-cut tune.

Several Republican senators will hold a press conference outside the Main Post Office, where thousands of Washingtonians will converge to beat the midnight deadline for filing 1979 tax returns, to denounce the tax policies and practices of the Democratic-controlled White House and Congress. And, as the Senate prepared to take up its budget resolution for 1981, the prospect of a "good behavior tax cut" is being held out by Democrats as a political plum to keep lawmakers from succumbing to the temptation to overspend.

One of the tax-cutters' chief targets is the Social Security payroll levy, which as risen proportionately faster than other major taxes in recent years and is scheduled for a big rate increase next year.

According to the Advisory Commission on Intergovernmental Relations, the Social Security tax is estimated to have absorbed 5.2 percent of the gross national product (the value of goods and services produced by the country in a year) in 1979 -- a nearly three-fold increase over the 1.8 percent that it took two decades ago.

The bite of the Social Security tax is thus only slightly less than the 5.6 percent of GNP that is taken by all state taxes and considerably more than the 3.6 percent of GNP that is captured by local levies of all kinds.

At the same time, revenues from federal excise taxes will balloon by more than 50 percent from 1980 to 1981, largely because of the oil tax that Congress approved earlier this year to recapture some of the proceeds from President Carter's gradual decontrol of domestic crude oil prices.

Carter's January budget projected that excise tax receipts would rise from $26.3 billion to $40.2 billion by 1981, compared with an individual income tax revenue increase of about 15 percent, from $238.7 billion to $274.4 billion.

Hence, although the individual income tax remains the biggest revenue-raiser by far, the tendency is away from the progressive income tax and toward more regressive payroll and excise taxes, increasing the burden of low-to-moderate-income earners.

Meanwhile, the Treasury Department reported that taxpayers -- eager for refunds that have swelled because of inflation -- have been filing their 1979 returns earlier than usual.

As a result, the department had to delay mailing about $3 billion in checks late last week because cash to run short.

As of April 4, the Internal Revenue Service had received 58.1 million out of 93 million anticipated returns, a 3.3 percent increase in the early return rate. The average refund was also up, from $490 last year to $590 this year.