Taxpayers seeking advice by phone from the Internal Revenue Service should be wary: even the IRS says a quarter of its answers to tax questions are inaccurate, and the General Accounting Office said yesterday that as many as 40 percent of taxpayers' telephone queries are answered incorrectly.

IRS Commissioner Lawrence B. Gibbs said the agency is "obviously not satisfied with answering only three out of four questions correctly at this time."

He said the IRS will continue monitoring the phone service and use the results to train employees to avoid those mistakes.

Rep. J.J. (Jake) Pickle (D-Tex.) said the apparent decline in accurate responses -- the GAO found that IRS operators answered questions correctly 79 percent of the time last year -- could undermine public confidence in the new tax system before it is even fully in place.

"When 25 percent of your calls are incorrect, that's an admission you've got a great improvement to make," Pickle admonished Gibbs during a hearing yesterday of the oversight subcommittee of the House Ways and Means Committee.

The IRS expects 22 million taxpayers to call for help this spring in coping with the alterations in the tax code enacted by Congress in 1986, a 30 percent increase from the previous year. More than 1,000 people and telephone lines have been added to handle the deluge, and workers who answer questions over the telephone have received training in the numerous changes in the tax law.

But when the GAO, a congressional agency, tested the system in 224 telephone calls over a period of six days, only 57 percent of the answers given to 20 hypothetical tax questions were fully correct.

Another four percent of the answers were correct, but mostly by accident: the IRS employee did not ask the proper questions to determine what the taxpayer's situation was. The other 39 percent of the questions were answered incorrectly.

GAO Associate Director Jennie S. Stathis told the subcommittee that the GAO's results were "very preliminary" and could not be projected to determine an absolute number of taxpayers who have received bad information from the IRS.

In general, the GAO survey praised the IRS' efforts to prepare for the implementation of the new tax law, although it pointed out that various tax forms were not available in all distribution sites.

The IRS survey of its own service encompassed 5,000 phone calls made since Jan. 1, asking 41 tax questions. Although Gibbs said at the hearing that the survey had found an accuracy rate of 74.8 percent, congressional sources said only 61 percent of the answers were fully correct and the other 13 percent were correct but not complete. On that basis, the accuracy rate as calculated by the IRS was only four percentage points higher than the rate found by the GAO.

Moreover, IRS officials have been saying privately that the accuracy rate has risen only recently to the 75 percent area, and was running closer to 60 percent earlier in 1988. Even an accuracy rate of 75 percent would mean that six million taxpayers have been misinformed by the tax collectors, according to congressional sources.

Another recent survey on IRS telephone accuracy, by Money magazine, found that 55 of 100 questions posed to IRS employees were answered accurately. Although many of the errors reported by the magazine were fundamental mistakes about relatively simple portions of the new tax code, the sample was not large enough to be representative.

Gibbs reiterated yesterday that taxpayers who rely on IRS advice in filling out their forms will not be prosecuted by the service if a mistake has been made, and any penalties will be waived. The taxpayer will have to pay the additional tax, although the service is looking into whether it can waive interest owed on the back taxes.

Gibbs said the IRS is working on guidelines to tell taxpayers how they can prove their errors were based on IRS misinformation, but an agency spokesman could not give a timetable for the release of that guidance.

Pickle, who chairs the subcommittee, said Gibbs was painting a "rosy picture" about IRS management of the current tax-filing season, which ends April 15.

"If I've given the impression it's all sweetness and light, that's incorrect," Gibbs responded. "But we've got a system in place to address the shortcomings."