The troubled 1985 filing season is almost over, but not forgotten. Rep. George W. Gekas (R-Pa.) has an idea for speeding future processing of returns and refunds by the Internal Revenue Service. In a House floor speech Tuesday, Gekas suggested staggering the deadline for filing tax returns so that millions of documents don't flood IRS offices at the same time.

Gekas soon will introduce legislation tying filing deadlines to a taxpayer's birthday. Taxpayers born between Jan. 1 and April 15 would file by April 15. Those born after that would file by the last day of the month of their birth. Married couples filing jointly could choose which birthday they want to use.

Gekas aides acknowledge a few problems that will have to be worked out, such as how to enforce the deadlines. But they are open to suggestions. Gekas would like to see the change included in the tax-revision legislation being considered in the House.

THE FORM'S IN THE MAIL . . . Recent tax bills have tended to involve intricate compromises that don't last long. An industry gives up something in one area so it won't lose as much in another. Then it comes back in the next Congress, finds some legislators who have forgotten about the compromise, and fights to get back what it gave up.

The newsletter Tax Notes reports that several lawmakers have introduced legislation to repeal part of a 1983 tax law intended to improve compliance with the tax code.

The law requires those paying out investment income, such as corporate dividends, to mail the check in one envelope and the taxpayer's copy of Form 1099 -- which tells the IRS how much money the taxpayer has received -- in another. The idea is to keep the 1099s from being discarded accidentally when the taxpayer takes the check out. The separate mailing prevents taxpayers from under-reporting their income, at least in theory.

Citing excessive paperwork and high mailing costs to the payers, Sen. William L. Armstrong (R-Colo.), Rep. D. French Slaughter Jr. (R-Va.) and Rep. Ben Erdreich (D-Ala.) have introduced bills to repeal the requirement. According to Tax Notes, they started out with support from the administration: Treasury Secretary James A. Baker III said his department could live with their bills.

Then Senate Majority Leader Robert J. Dole (R-Kan.), who was chairman of the Senate Finance Committee when the law was passed and is a stickler for tax compliance, said in a letter that it was part of a "carefully drawn compromise to improve tax compliance." Last month, Assistant Treasury Secretary Ronald A. Pearlman wrote Slaughter that the department would not support any specific legislation until it analyzed the effect of the requirement.

ONE BACKLOG DOWN . . . The good news is that the IRS has reduced its backlog of pending regulations. The bad news is that the inventory of unfinished rules, at 446, still is at a historic high.

Just before President Reagan's tax cut was passed in August 1981, the IRS had a total of 297 pending regulations on the shelf. Three major tax laws in the last four years have increased the number of unfinished rules.

But there are still rules hanging over from earlier tax laws. In addition, IRS officials sometimes decide that additional regulations are needed, and new laws can disrupt efforts to rewrite rules.

For instance, during August, the most recent month for which figures are available, the IRS completed action on eight regulations and opened up four new cases -- a net decline of four regulations.

PEOPLE . . . The IRS has made personnel changes at several of the service centers that had the most problems with their computers and processing refunds this year.

At the Philadelphia center, Joseph H. Cloonan has been appointed director, a post he filled on an acting basis during much of the past year. Cloonan replaces Norman E. Morrill, who is now on the staff of the mid-Atlantic regional commissioner after working on a task force at headquarters. Cloonan came from the IRS center at Andover, Mass., where he has been replaced by Thomas Quinn, who previously worked at IRS headquarters here.

The Austin, Tex., service center, where 20,000 letters from taxpayers were inadvertently shredded, is now run by Larry Westfall. He replaced G. William Grabow, who retired. In Atlanta, which experienced no unusual processing problems, Sylvia H. Wren has replaced retiring William B. Hartlage.