IRS employees put in overtime, post offices set up special mail drops and demonstrators made their cases as the nation prepared to end another federal tax return filing season at midnight Monday.

Internal Revenue Service spokesman Frank Keith said the IRS had no way of knowing how many taxpayers were waiting until the last minute to file. But the agency expects to receive 18 million returns this week, including those filed over the weekend, he said.The deadline is one day later in New England and most of upstate New York because Monday is Patriot's Day, a legal holiday, in Massachusetts, site of the IRS center that processes returns from taxpayers in those states.

The IRS expects to receive more than 109 million returns this year, many of which will come in well after the deadline.

About 6 million couples and individuals are expected to get an extra four months to file - but not to pay any taxes due - by mailing Form 4868 before midnight. Many of the 650,000 Americans who live and work abroad are likely to take an automatic two-month extension. And, as usual, some taxpayers simply will miss the deadline and face a late-filing penalty.

The Postal Service was doing its part by setting up booths at ballparks, selling stamps by the curb and cooperating with radio stations and civic groups that were offering refreshments around post offices in an effort to make things a little easier for procrastinators.

Around the nation, the Jobs for Peace Campaign sent demonstrators into the streets to protest military spending. They planned to pass out "Build Homes - Not Bombs" stickers for taxpayers to attach to the envelopes containing their tax returns.

In Washington, Sen. Mark Hatfield, R-Ore., repeated a tax-day act he has performed for 10 years: introducing a bill that would allow conscientious objectors to pay their taxes into a fund that would be spent for non-military purposes.

The National Treasury Employees Union, which represents most IRS employees, issued a statement accusing the Bush administration of failing to budget enough money to finance the tax-collection agency. Employee travel and training have been cut and technicians have been pressed into clerical work because of the tight budget, said Robert M. Tobias, president of the union.

The Church of Scientology used the filing deadline as a way of reminding taxpayers of a new law designed to protect them when they have disputes with the IRS. The church, which has had its share of scraps with the agency, announced it has published a free guidebook to the "Taxpayer Bill of Rights."