The Internal Revenue Service said yesterday that it is continuing to run well ahead of last year's disastrous performance in processing income tax returns, and IRS officials predicted that no serious problems would develop between now and next week's filing deadline.

The number of returns filed so far has been slightly below the number of returns filed at this point a year ago, but processing is well ahead, said IRS spokesman Rod Young.

Compared with 36,142,000 returns processed by April 5 last year, the service had processed 45,969,000 as of April 4 -- an increase of 27.2 percent.

Compared with 27,513,000 refunds certified by April 5, 1985, the IRS has certified 36,280,000 -- a 31.9 percent increase.

"Everything is moving right as normal," said Young.

He said the IRS is giving priority to issuing refunds by June 1, the date after which interest is owed to taxpayers. "We expect to certify 69 million refunds prior to June 1," he said.

"We're close enough that the filing crunch will not be unmanageable," Young said.

Refunds are generally being paid within six to eight weeks, he said.

"It looks pretty good," said a spokesman for Sen. John Heinz (R-Pa.), whose office received a barrage of complaints last year about the Philadelphia Service Center, which handles tax returns from the District and Maryland. Virginia returns are processed in Memphis.

Operations in Philadelphia and elsewhere appear to have improved, said Heinz's spokesman, who said that inquiries and complaints to the senator's office are down.

"We're back to the usual level," he said. "It's not like it was last year."