Treasury Department officials notified the Senate and House Appropriations committees yesterday of their intention to drastically cut the taxpayer assistance program and toll-free telephone tax advice on Nov.1 despite strong congressional signals not to tamper with the popular services.

Congressional sources said if the administration moves ahead with the plan as outlined to them, as many as 1,500 IRS workers could be RIFfed (fired) or moved to other jobs starting next month.

Before adjournment last month the Senate and House committees approved a continuing budget resolution for the Treasury Department that restored $50 million cut from the taxpayer-assistance program by President Reagan's budget. The House budget specifically earmarked the funds. The Senate unit's report stated that the program should continue. The full House and Senate, however, have not acted on the committees' recommendations.

Administration officials have proposed that use of the toll-free number taxpayers now call for tax questions be limited to specific questions about accounts, and not used for general information on how to prepare tax returns. Earlier this year the IRS closed a number of walk-in offices where taxpayers could get assistance.

A Treasury source who asked not to be identified said the administration plan is to "expand taxpayer assistance" in other ways such as training "community groups" to provide taxpayer information and to "enlarge media programs" to answer general tax questions.

Congress will not return for its special lame-duck session -- to work on agency budgets -- until after the November elections. If Treasury moves quickly with its plan to eliminate or reshape the taxpayer service program, much of it could be dismantled -- and many if its employes transferred on put on the street -- before Congress would have a chance to block it.

The National Treasury Employees Union, which represents IRS workers, was contacted yesterday by the IRS and advised of the proposed cutback. NTEU had persuaded the Senate and House to restore taxpayer assistance budget cuts proposed by the president.

NTEU President Vincent L. Connery said his union "deplores this action [to cut the service] which is in direct contravention of the will of Congress."

Connery said "it is typical of this administration to cut the services which the government provides its citizens, those most used by the poor, the elderly and the working class. It is outrageous that this administration continues to ignore the will of Congress. We have already contacted the Senate and House Appropriations committees seeking their assistance in stopping the administration plan and we are also exploring the possibility of legal action."