Changes in airport security: No curbside check-in allowed. Only passengers with tickets in hand are allowed to the gates. Parents can escort children flying alone to the gates. No electronic tickets are accepted at the gates. No knives of any type or size are allowed on aircraft. This includes all pocketknives, carpenter's knives and retractable blades. Some parking spaces have been lost because of an off-limits zone set up around the main terminal. Travelers should arrive several hours early for check-in and should not come to the airport unless they have received confirmation of their flight's status by their airline.

Officials resumed partial service of the world's busiest airport only after significantly strengthening their security systems in the wake of four terrorist hijackings Tuesday.

The Federal Aviation Administration grounded all flights and closed all the nation's airports after the hijacked planes crashed into the World Trade Center towers in New York and the Pentagon in Washington.

The security changes - ordered for all American airports by the FAA - have done away with curbside check-in and parking within several hundred feet of airport terminals.

The result for travelers is long check-in lines, constantly changing arrival and departure times and, for many, confusion.

''It's going to be a while before we're back to 100 percent,'' said Yolanda Clark, Hartsfield's assistant manager of public relations.

Joanie Synder of Atlanta did not know about the suspension of curbside check-in until after she arrived to drop off her grandfather.

''When we pulled up outside, I said, 'Oh Grandpa, look. This is going to be easy,''' she said. Once inside, however, the Synders found themselves in line with hundreds of others.

Airport officials told travelers to expect long waits - easily in excess of two hours just to make it through the 300-plus person check-in lines.

Most travelers, however, remained calm and patient Thursday, many just happy to be in the airport after spending two days in local hotels.

More than 280 people were in front of Trevor Phillips in the Delta Air Lines check-in lines. Yet Mr. Phillips wasn't too bothered by the wait.

''I don't have a problem with it,'' said the businessman, stranded in Atlanta while en route from Washington to Dallas.

''It's something we have to put up with,'' he said, praising the new security measures.

The FAA's new guidelines also mean that only passengers with tickets will be allowed past the security gates leading to the airplane terminals.

Children flying unescorted, however, can be accompanied to the gates by their parents.

As check-in lines swelled Thursday afternoon, travelers found ways to pass the time. Some swapped stories of the past several days, telling where they were supposed to have gone.

Others napped on couches, chairs and even the occasional luggage carousel.

The various airlines had dozens of personnel on hand to answer travelers questions about the new security procedures.

Some rumors even began to spread through check-in lines in the early afternoon, with travelers receiving false information that carry-on luggage was prohibited and entrance to the terminal gates was allowed only within four hours of takeoff.

Reach Brian Basinger at (404) 589-8424 or mnews@mindspring.com.