NEW YORK — The selfless spirit that helped mend a stricken nation eight years ago was renewed. Volunteers marked 9/11 on Friday by tilling gardens, writing letters to soldiers, setting out flags — and, at ground zero, by joining the somber ritual of reading the names of the lost.

President Obama, who observed his first Sept. 11 as president by declaring it a national day of service, laid a wreath Friday at the Pentagon and, with his wife Michelle, helped paint the living room of a Habitat for Humanity house in Washington.

“We honor all those who gave their lives so that others might live, and all the survivors who battled burns and wounds and helped each other rebuild their lives,” Obama said. He said the day was meant also as a tribute to the “service of a new generation.”

Memorials in New York, at the Pentagon and at the crash site of United Airlines Flight 93 in Pennsylvania all took place under gray skies. A chilly rain fell in lower Manhattan, and those reading names at the World Trade Center site spoke under tents.

“We miss you. Life will never be the same without you,” said Vladimir Boyarsky, whose son, Gennady Boyarsky, was killed. “This is not the rain. This is the tears.”

In the hours after the attack and for weeks afterward, volunteers responded to New York City’s needs, sending emergency workers to help with the recovery, cards to victims’ families, and boxes of supplies.

“Each act was a link in a continuous chain that stopped us from falling into cynicism and despair,” said New York Mayor Michael Bloomberg.

Across the country, Americans marked the anniversary with service projects.

Volunteers in Boston stuffed packages for military personnel overseas. In Tennessee and West Virginia, they distributed donated food for the needy. Community volunteers in Maine worked on a garden and picnic area for families transitioning out of homelessness.

In Chicago, they tilled community gardens, cooked lunch for residents of a shelter and packed food for mothers and babies. And on the lawn of the Ohio Statehouse, volunteers arranged nearly 3,000 small American flags, in a pattern reminiscent of the trade center’s twin towers. At the top was an open space in the shape of a pentagon.

At a plaza adjacent to the World Trade Center site, volunteers — from soup kitchens, advocacy groups, the Red Cross, the United Way — joined relatives of the lost to read the names of those killed in the twin towers.

“I ask that you honor my son and all those who perished eight years ago . . . by volunteering, by making some kind of act of kindness in their memory,” said one of the readers, Gloria Russin, who lost her son, Steven Harris Russin.

Theresa Mullan, who lost her firefighter son, Michael, wore a poncho and shivered in the rain as she waited for her son’s name to be called. She said she couldn’t dream of being anywhere else.

“It’s a small inconvenience,” she said of the weather. “My son is the one who ran into a burning building.”

Moments of silence were observed at 8:46, 9:03, 9:59 and 10:29 a. m. — the precise times that jetliners struck the north and south towers of the trade center and that each tower fell.

At ground zero in lower Manhattan, relatives and friends of victims visited a partially built, street-level Sept. 11 memorial plaza that had not been there a year ago.

The memorial, to be partially complete by the 10th anniversary in 2011, will ultimately include two square pools evoking the towers’ footprints, with victims’ names surrounding them and waterfalls cascading down the sides.

On Friday, William Weaver placed a single red rose in a temporary reflecting pool at the plaza, a photograph of his son, policeman Walter E. Weaver, pinned to his jacket. He said the memorial was taking too long and he did not like it. “It should have been a graveyard-type of thing,” Weaver said.

In Shanksville, Pa., bells tolled for the 40 victims of the fourth hijacked jetliner that crashed there.

Eight years after 2,976 perished in the attacks, Obama vowed at the Pentagon that the United States “will never falter” in pursuit of al-Qaida. “Let us renew our resolve against those who perpetrated this barbaric act and who plot against us still,” he said.