The Internal Revenue Service and the union for most of its 100,000 employees announced a program to improve service to taxpayers by spotting potential problems in advance. Commissioner Lawrence B. Gibbs said the IRS is the first federal agency to directly involve employees in upgrading service. In return for their efforts, IRS employees are expected to see a higher-quality work life. Gibbs acknowledged that IRS service has had faults, highlighted by declines in ability to correctly answer taxpayer questions and by delays in processing returns. He put part of the blame on a constantly changing tax law, inadequate funding and the need to increase reliance on changing computer technology.