WASHINGTON — It’s time to start that “to do” list for holiday cards and packages. The U.S. Postal Service reminds customers that deadlines for sending holiday packages are approaching, particularly for those going to U.S. troops in Iraq and Afghanistan.

To arrive before Christmas, mail going to members of the military in Iraq and Afghanistan should be sent by Dec. 4. Military mail headed to other overseas destinations should be sent by Dec. 11, the Postal Service said Tuesday.

“We have so much mail for the troops over the Christmas holidays,” said Pat Donahoe, deputy postmaster general and chief operating officer. “We are very, very cognizant of the importance that the mail has to the military.”

Those sending cards and packages within the United States have a little more leeway.

The Postal Service’s suggested deadline for sending domestic packages using the least expensive option, parcel post, is Dec. 15. For parcels sent first class or priority mail, the deadline is Dec. 20.

Customers have until Dec. 22 to send Christmas packages by express mail.

The Postal Service expects to deliver about 20 billion cards, packages and letters between Thanksgiving and Christmas. It predicts that the volume processed each day will reach a peak of about 1 billion on the busiest day, Dec. 17. Most of this mail should be delivered two days later.

Donahoe advised customers sending all holiday packages to remove batteries from electronic items because they could turn on, which could prompt postal employees to open the package for inspection. People should not tie packages with string, as that, too, could cause shipping problems. Donahoe also suggested placing a backup tag inside each package that specifies both the shipping and return addresses, in case the outer label gets damaged.

To request a free package pickup, purchase stamps, hold mail and design holiday cards, go to www.usps.com.

The Postal Service also said that it is continuing its program of allowing individuals and businesses to answer the requests from needy children. Every holiday season, the post office receives “hundreds of thousands” of letters addressed to the North Pole.

As of last year, those who want to respond to the requests must sign up in person at a post office and present state or federal identification. They are also required to fill out a form stating their name, address and the letters they are adopting.

“Our goal completely is to guarantee the safety of these children,” spokeswoman Sue Brennan said.