IRS personnel gave the correct answer on only 64 percent of telephoned tax queries, and government auditors say a major reason was a failure to press questioners for details.

A survey by the General Accounting Office, involving 1,733 test calls during the last return-filing season, also found the IRS was even less likely to give the right answer on questions affected by recent changes in tax law."IRS assistors' failure to probe for all of the pertinent facts before answering GAO's questions was a primary reason for the 36 percent inaccuracy rate," the congressional watchdog agency said in a report to Congress. "Of 20 test questions, 17 required assistors to probe to correctly understand and answer the question."

When answers to only those 17 questions are considered, the IRS was wrong 39 percent of the time. Questions requiring no further details produced correct responses 78 percent of the time, the GAO reported.

The GAO emphasized that the inaccurary rate applies only to the specific questions that were asked - and not necessarily to all the questions taxpayers are likely to ask. However, the IRS's own check of actual taxpayer calls last spring indicated its telephone personnel provided the correct answer just 72.4 percent of the time.

IRS Commissioner Lawrence B. Gibbs, in responding to the latest GAO report, said the IRS was well into a program to improve the skills of the telephone "assistors" before the current filing season.

"We . . . have expanded assistor training on probing skills," Gibbs said. "In addition, we continue to emphasize to all managers the need for quality review and providing immediate feedback to assistors who fail to probe completely."

The IRS answered 20 million calls on its 4,359 toll-free assistance lines last year. That represented about 85 percent of the direct contact the IRS had with taxpayers.

Most telephoned questions are answered by "front-line assistors," who often are part-time employees earning $6.50 to $11.70 an hour. If they cannot answer a question, they are supposed to turn the caller over to a backup assistor, who has received more training, has more reference material close at hand and who is paid up to $14.32 an hour.

However, the GAO survey indicated that the backup assistors gave the wrong answer to 40 percent of the questions, compared with 35 percent for the front-line employees.