Amid cheers, marching-band music, and confetti, millions of spectators squeezed onto packed sidewalks along Amsterdam Avenue and Broadway yesterday to mark the official start of the holiday season with the 78th annual Macy’s Thanksgiving Day Parade.

Led by a giant blue “Super Grover” balloon that towered above its waving handlers, the parade kicked off just after 9 a.m. and wended its way down the West Side toward Herald Square.

This year, Macy’s unveiled several new additions to its parade repertoire, including a much-anticipated, 16,200-cubic-foot, helium-filled SpongeBob SquarePants, the first square balloon to be added to the lineup. Red and Yellow M&Ms and Chicken Little also made their debuts, and the four new balloons vied for most-favored status against such old standbys as Clifford and Ronald McDonald.

The parade lineup this year consisted of 59 balloons, including 15 of the popular giant variety; 10 marching bands; 27 floats, and 30 groups of clowns. Between 8,000 and 10,000 people are required to organize it, said Elina Kazan, director of publicity for Macy’s East.

“This is the epitome of the Thanksgiving holiday,” Christine Photos of Pittsburgh said. She not only attended the parade but also braved the rain to observe the balloon-inflation proceedings on the Upper West Side the night before.

After the previous evening’s winds and intermittent drizzle, organizers of the parade feared that the 15 largest balloons might be grounded during the event. Yesterday, however, unusually warm temperatures and even moments of sunshine greeted parade organizers, spectators, and participants as they marched the length of the 2 1/2-mile route.

Guidelines restricting the use of the large balloons on windy days were put in place after a spectator was seriously injured in 1997 by a balloon that was blown off-course during the parade.

The possibility of bad weather proved not to be a deterrent to the estimated 2.5 million spectators who lined the parade route, some arriving as early as 6:30 to stake out a claim for a prime viewing position. One woman, Ashley Forshee, welcomed the warmer-than-expected temperatures but had come prepared for the worst, bundled in layers of yellow Gore-Tex and gray fleece. “We came two years ago and it was really cold,” she said, “so as you can tell we were ready for more of the same.”

Nor did the notorious New York weather keep Barbara Deery and Betsey McMillan, both of South Carolina, from awakening at 5:30 to nab their front-row location on Broadway and 40th Street. Complete with folding chairs and a canister full of caramel popcorn, the mother-daughter duo enjoyed their first live Thanksgiving Day Parade.

“It was really different than on television,” Ms. Deery said. “You get so close to the people carrying the balloons, and they look like they’re having a great time. I’ve never thought about them before.”

Parade-goers who arrived later jockeyed fiercely for position in crowds that at points measured 15 people deep. Some stood on folding chairs, stepladders, or building stoops, or climbed atop the concrete tree planters that line the streets, to view the festivities.

Spectators also lined the landings of the new Time Warner Center at Columbus Circle in hopes of catching a glimpse of the floats through the picture windows as they turned from Amsterdam onto Broadway.

But others didn’t like the bustle of the crowds.

“I kind of like seeing it on TV with my cup of coffee. It’s pretty crowded here and hard to get in,” said Kim Peterson, who flew in from Minneapolis to visit family.

Ms. Kazan, the publicity director, disclosed no secret viewing locations. “I think the parade is beautiful anyplace you see it,” she said. “But viewing it against the trees of Central Park West is especially beautiful.”

Mayor Bloomberg demonstrated more concern yesterday for city workers and the elderly than for parade viewers. He stopped by a 911 center in Brooklyn to visit workers who were fielding emergency calls on the holiday and said he was “thankful that the city’s doing well.”

The mayor said he was also thankful for his family and planned to eat a turkey dinner with his two daughters in the late afternoon.

On the subject of the Macy’s parade, in which he did not march, his comments were brief. “Charlie Brown is my favorite balloon,” Mr. Bloomberg told reporters, “so I can save you the question.”