Last week’s fizzled Christmas Day terrorist attack on Delta/NW Flight #253 from Amsterdam to Detroit ignited a wave of new security measures at airports and on airplanes.

Airport and airline spokespeople and TSA officials say domestic passengers will likely notice some heightened security procedures, such as explosive-sniffing dogs and added law enforcement presence at many domestic airports.

Travelers on US-bound flights, though, will be notice significant changes.

Under rules rushed out over the weekend, passengers boarding flights heading to the United States will be subject to pat-downs and bag searches at the gate.  During their flight, passengers will be required to put away personal items and stay in their seats for the final hour of flight.

The TSA posted a very general description of the new rules.  More specifics were posted on various airport and airline Web sites and detailed in a memo that some airlines shared with bloggers over the weekend.

Bottom line:

While everyone gets used to the new regulations, get to the airport early. Really early.

If you’re flying internationally to the United States, be prepared for an extra pat down and bag check at the gate.  And pack carefully:  you’ll only be allowed one small – very small – carry-on bag.

It’s a good bet that airlines, airports and the TSA will make some changes to rules and procedures starting today, so keep an eye on the news, airline and airport Web sites, and the TSA.gov site.

Rules are already changing:

Last night Canada’s WestJet announced that it would no longer accept roller bags or larger backpacks as carry-on luggage. And this morning American Airlines announced that, due to the long lines and confusion over the new rules, for the next few days the airline will waive change fees for passengers traveling from Canada to the United States.  Other airlines will probably do the same.

Here’s a link to the story on the new rules I wrote for MSNBC.com.

Please share your stories about your travel experiences this past weekend and let us know what you see happening if you end up stuck at the airport.