The Internal Revenue Service gave a lot of inaccurate information last year to callers on its toll-free phone line _ and may be doing an even worse job of answering questions in 1989.

Internal surveys show an error rate of 30.8 percent so far this year, slightly higher than the 27 or 28 percent reported in less reliable surveys in 1988."We're not pleased with our performance in respect to accuracy," said Robert LeBaube, director of taxpayer services for the IRS. He blamed the increasing complexity of tax law. The big changes came in the Tax Reform Act of 1986, but there have been 13 other modifications since then, he said.

This year's error rate is higher than expected, considering the fact that 1988 tax forms do not differ substantially from the 1987 forms. Even so, said LeBaube, telephone assisters must be much better trained than they were in the 1950s and 1960s.

"A simple question on the dependency exemption can require as many as 42 probing follow-up questions to get the correct answer for a particular taxpayer in a particular set of circumstances," he said.

The survey found that questions involving capital gains, pensions and deferred compensation are especially troublesome to the 5,000 assisters who handle toll-free calls for the IRS.

"We're not alone in this," said LeBaube. "Paid preparers are having problems with them, too."

The IRS assisters, about 1,500 of whom are new this year, are initially trained for five weeks and receive as much as a year's training if they remain in the system, LeBaube said.

Assisters tend to be high school graduates, some with college credits, who earn roughly $16,000 to $24,000 a year. None is an accountant or tax lawyer.

"I don't think the economy would support giving us 5,000 tax accountants," LeBaube said.