Barely a month before income tax returns are due, the Internal Revenue Service is giving wrong answers to approximately one of every three questions it gets over its toll-free telephone lines, IRS officials said yesterday. The agency's error rate of 30.8 percent so far this year is even worse than it was last year, when IRS assisters got 27.6 percent of the answers wrong. Accuracy has declined despite the fact that the service has received 1 million fewer calls than it did by this time last year, and has had another year to digest the major tax law overhaul of 1986. "We are not pleased with our performance with respect to accuracy," said Robert LeBaube, IRS director of taxpayer services. The IRS is taking steps to improve its answers and "we are very hopeful that the percentages of error will go down over the next several weeks of the filing season and continue to go down as we make changes," he said. However, the situation may be even worse than the IRS statistics indicate. Preliminary figures supplied by Congress' General Accounting Office to a House subcommittee suggest that over the past two weeks, at least, the IRS was wrong 40 percent of the time. "We have some serious questions about the accuracy and validity of the data" put out by the IRS yesterday, said a spokesman for subcommittee chairman Doug Barnard (D-Ga.). The IRS figures come on the heels of a another recent GAO report that found errors in 31 percent of taxpayer correspondence cases during fiscal 1987. These are cases in which the IRS has asked the taxpayer for information or has determined a deficiency. A spokesman for Sen. David Pryor (D-Ark.) pointed out that the Reagan and Bush administrations both have proposed charging taxpayers a fee to use the IRS telephone-assistance service -- hardly a bargain if one-third of the answers are incorrect. "What are they going to do when they get it wrong?" he asked. "Give you a rebate?" Rep. J.J. Pickle (D-Tex.), chairman of the House Ways and Means oversight subcommittee, called the error rate "unacceptable" and said it "must be corrected immediately." In its defense, IRS officials pointed to the growing complexity of the nation's tax laws and the numerous and rapid tax-code changes that have been made in recent years. LeBaube said Congress has passed 138 bills affecting taxes since 1976, 13 of them since the Tax Reform Act of 1986 and eight in 1988 alone. To illustrate the complexity of some provisions of the code, he said that a question on claiming an exemption for a dependent can require the IRS employee to ask as many as 42 questions of the taxpayer before the correct answer can be determined. Furthermore, he said, the IRS has developed tape-recorded messages to respond to many of the simpler questions that formerly increased the service's batting average. He said today's questions are harder and take longer to answer. Although there is widespread concern over the IRS's ability to hire and retain quality employees at its current pay scales, LeBaube declined to criticize the agency's 5,000 telephone answerers. They are all at least high school graduates, and some are college graduates, he said. Their employee grades range from GS-5, with starting pay of $15,738 a year, to GS-9s who are paid up to $31,000 annually. Many of the workers at the low end of the scale are part-time, seasonal employees. Some 1,500 of the 5,000 answerers are new this year, he said. All have had at least five weeks of training, and are required to stay within the subjects they know when answering questions. If the question ranges outside their knowledge, they are supposed to refer it to a more experienced person. LeBaube acknowledged that the people who answer calls are not accountants or lawyers. However, he pointed to a recent Money magazine article in which 50 tax professionals sampled all gave different answers to a question about a complex tax situation, most of them wrong. "I don't think the economy could support giving us 5,000 tax accountants" to answer the phone, he said. He said that answers involving exemptions for dependents have improved this year after receiving special emphasis in training, but questions on capital gains, pensions and deferred compensation remain soft spots, he said. "We are not out to cause pain and suffering" to taxpayers, he said.