Internal Revenue Service Commissioner Roscoe L. Egger Jr., who spends a lot of time hearing complaints from angry legislators about late tax refunds and lost letters, will get a chance this week to show them how tough it is in the field.

The House Ways and Means subcommittee on oversight, chaired by Rep. J.J. (Jake) Pickle (D-Tex.), will travel to the IRS's Fresno, Calif., service center. Sixty thousand letters were recently shredded at the Fresno center, even though the taxpayers involved had not been notified that their cases had been settled in their favor.

Egger told a subcommittee hearing Friday that the visit would show members just how difficult it is to keep track of millions of returns, especially with a balky new computer system that was spitting them out on a regular basis, particularly in the early filing season.

Pickle, whose Austin district includes one of the agency's 10 service centers, indicated that it would take a lot of persuasion for him to accept this year's foul-ups.

"I've been to Austin," he said. "I'm going to Fresno. I'm even screwing up my courage to go to Philadelphia," which reportedly has had the most trouble processing returns.

TAXING FREQUENT FLYERS . . . The service is not exactly rushing to decide whether "frequent flyer" airline flights should be taxed as income if they were earned through business travel paid by the passenger's company. Technically, the IRS says such flights constitute taxable income, but without regulations setting reporting and enforcement rules, taxpayers are unlikely to cough up.

For several months, the service has been trying to decide whether rulings or regulations are necessary, but it hasn't made a decision, spokesman Ellen Murphy said. In theory, forthcoming final regulations on the tax treatment of fringe benefits could include frequent-flyer requirements, but it would be unusual to make such a proposal as part of a batch of final, rather than proposed, regulations, Murphy said.

Meanwhile, Rep. Harold E. Ford (D-Tenn.) has gained a little support for his legislation to treat the flights as income. Three members have signed up as cosponsors, and a group of regional airlines, which doesn't like the plans because its members generally don't offer them, is organizing to lobby for the bill. If the bill is considered this year, however, it probably will be as part of a broad effort to revise the tax code.

BUDGET UPDATE . . . Ways and Means members have been openly critical of the Reagan administration's proposal to trim 1,254 IRS staff positions in fiscal 1986 at a time when taxpayers have to cope with busy signals and unanswered correspondence. The administration wants to add 2,500 examiners to improve compliance -- but not until fiscal 1987.

On Wednesday, the House Appropriations subcommittee on Treasury, Postal Service and general government will get a chance to change all that. The committee is to mark up the IRS 1986 appropriation, among other provisions. Members will have before them the administration proposal for $3.5 billion for the agency, and a letter from Pickle, Ways and Means Chairman Dan Rostenkowski (D-Ill.) and Rep. Richard T. Schulze (R-Pa.) seeking an additional $115 million for 1,500 more staffers and some new computers.

The omnibus supplemental appropriations bill that has been passed by the House and Senate in different forms includes another $33 million for the IRS, mostly to cover salaries of current employes.