The Internal Revenue Service is trying once again to cut back toll-free telephone service for taxpayers, but Congress is almost sure to block the move.

Last year, congressional opposition to a $50 million reduction in taxpayer services was so strong that the legislation not only retained the money, but included language ordering that telephone advice be continued.

This year, IRS Commissioner Roscoe L. Egger Jr. has told a House Appropriations subcommittee that elimination of the telephone service would save $25 million and eliminate 986 jobs,, but he ran into opposition from subcommittee Chairman Edward R. Roybal (D-Calif.).

"The average person who needs help thinks of picking up the telephone and calling the IRS," Roybal told Egger. "The taxpayer who needs help will not get it, then he will say the hell with it and not file a tax return at all."

Egger contended that eliminating the service would result in "a more cost-effective and streamlined system for providing essential information to the public." He argued that it is difficult to determine the worth of the telephone service, which would be replaced by a number of other expanded activities.

"We are emphasizing the use of pre-recorded tax information coupled with an outreach program which expands the use of walk-in services to the public through more accessible sites at more accessible hours," he said.

In addition, the IRS would continue "televised tax clinics to aid large numbers of taxpayers in the preparation of their returns, as well as targeted broadcasts to certain groups such as Spanish-speaking and elderly taxpayers," he said.

The IRS chief noted that a preliminary survey by the General Accounting Office showed that 6 percent of the persons using the telephone service are tax preparers, and many others are college graduates, who presumably have less need of telephone advice.

But the service is popular with constituents, and although the legislative process has just begun, it appears highly unlikely that Congress will eliminate it.

The IRS also has irritated Roybal with a separate proposal to divide the two California IRS districts into as many as six separate districts.

Egger told Roybal that "the growth and trends in California necessitate expanding the districts" to achieve more efficiency. Roybal countered that such a move will be opposed by the entire California House delegation.

INTERPRETERS NEEDED . . . One of the thorniest provisions in last year's tax bill, the Tax Equity and Fiscal Responsibility Act of 1982 (TEFRA), was a section restricting the tax breaks available to beneficiaries of pensions, particularly the huge tax deferrals that could go to persons with high incomes.

The IRS has been struggling to put out regulations ever since, while pension-plan administrators have been trying to revise programs to meet the new rules.

This month, the IRS has been issuing extensions to give administrators more time to make their pension plans conform to the new law.

The complexity of the process is reflected in a proposed regulation issued by the IRS last week for certain kinds of pension plans. In a question-and-answer format, the proposed regulation asks and answers at great length 50 questions, including "What is a permissive aggregation group?" and "What plans will be treated as top-heavy if a permissive aggregation group is top-heavy?"

The process is creating a bonanza for accounting firms, many of which have been sending warnings to clients with pension plans that they will need sound advice to deal with the new law.