Don't look now, but Friday is T-day that day that inevitably rolls around the middle of every April when federal and state income tax returns are supposed to be filed.

And as is usually the case, thousands of Utah taxpayers are putting off filing until the last minute.Luckily, procrastinating Utahns will still be able to take their returns to any one of 20 post offices as late as midnight April 15 and still get that day's postmark. Usually only the Main Post Office in Salt Lake City gives the same day's postmark to letters mailed very late in the day.

Dennis Yuhl, Salt Lake City Division general man-ager/postmaster, said people mailing their returns late should take them to collection boxes located directly outside of post offices with the extended hours.

Midnight collection in and around Salt Lake City will be provided at: The Main Post Office, 1760 W.

21st South; the Holladay Branch, 2350 Arbor Lane; Downtown Station, 230 W. Second South; South Salt Lake Branch, 3161 S. West Temple; Sugarhouse Station, 2155 Highland Drive; Murray Branch, 4989 S. State; and the West Valley City Branch, 3490 S. 44th West. Midnight collection will also be provided in the outlying areas of the valley. These include: Sandy, 8850 S. Seventh East; Bountiful, 750 S. Main St.; and West Jordan, 1800 W. 78th South.

Similar service will be provided in Ogden at the Main Post Office, 3680 Pacific Ave.; the Town Station, 2641 Washington Blvd; and the Ben Lomond Station, 506 Washington Blvd.

Collection until midnight will also be offered at the main post offices in Cedar City, Logan, Price, Provo, Richfield, St. George and Vernal.

Meanwhile, the Utah State Tax Commission offices are also gearing up for a flood of last-minute state tax returns.

By midnight April 15, nearly 600,000 Utah income tax returns are expected to be in the mail or already at the Tax Commission offices, said commission spokesman Lee Shaw.

As of April 8, the commission had received 280,062 individual income tax returns up 44,525 from 1987.

He said even with new automated mail handling equipment, it will take until about May 6 to process all the 1987 returns.