A growing amount of tax money withheld from workers' paychecks is being misused by employers, often never finding its way to the government, the Internal Revenue Service said yesterday.

The total of these delinquent Social Security and income taxes rose by 49 percent from 1982 through 1987, to almost $3.73 billion, said William M. Wauben, assistant commissioner for collections at the IRS. About 338,000 employers have failed to pay or account for that money.

Because withheld taxes make up 69 percent of all federal revenue, "even a slight decline ... can have a devastating impact" on the government, Wauben said.

The IRS also announced that although fewer individual taxpayers are filing their returns early this year, the pace is picking up. Through Feb. 26, 30.2 million returns had been filed, down 4.9 percent from a year ago. But last week, the IRS received 6.7 million, up 3 percent from the same week in 1987.

The IRS speculates that taxpayers are delaying filing this year because of changes caused by the Tax Reform Act of 1986. The filing deadline is April 15.

The number of returns qualifying for refunds is down 4.5 percent to 7.55 million this year. However, the average refund is $793, up from $735 a year ago.

The failure by employers to forward taxes withheld from workers' checks often is caused by ignorance of the law, Wauben said, although in some cases withheld taxes are kept out of greed. The problem usually is traced to a failing company's efforts to stay afloat, he said.

"When employers find they are no longer able to keep their business operating on the cash available and they ... are unable to borrow from a bank or other lending institution, some begin using the funds withheld from their employees' wages as their own," Wauben said.

Employers are required to turn over withheld taxes to the government at least once a quarter. Some large companies pay the IRS every three days, though most employers file employment-tax returns weekly or every two weeks.

An employer's misdeed does not necessarily cause a problem for workers. Even though workers' withheld taxes might never be turned over to the government, their accounts will be credited by the government as long as they file an income tax return.

A new IRS program aimed at another route of tax evasion has produced good results, Wauben said. This involves the practice by some employers of wrongly classifying some workers as independent contractors.

In the case of these independent contractors, an employer does not withhold Social Security and income taxes from the workers, though they are required to make quarterly estimated tax payments. However, many such workers often understate earnings, and some don't even file returns, the IRS says.

During a two-year study in 26 areas of the nation, IRS officers audited 1,196 employers suspected of misclassifying workers as independent contractors. As a result, 9,004 delinquent quarterly tax returns were filed and the IRS hit 92 percent of the audited employers with tax bills averaging $3,000.