The Occupy D.C. encampment in McPherson Square had a forlorn, empty feeling Saturday afternoon as members of the diminishing tent colony warmed themselves in the winter sunlight and contemplated the likelihood that they would shortly be forced to leave a patch of ground that has become their home for months.

But late Saturday night, many of them took part in vigorous demonstrations outside a formal dinner held nearby and attended by President Obama.

Officials of the National Park Service, who had been fairly lenient, announced Friday that on Monday they will begin fully enforcing regulations against camping overnight in federal parks. Those rules ban bedding or lying down to sleep in parks at night.

Some campers spoke defiantly Saturday of staging a “sleep strike,” or remaining in the park at night without lying down, in narrow compliance with the rules. Organizers also said tents would still be allowed as long as they kept one flap open and did not turn them into winter burrows.

“It’s going to be up to each individual, but we will definitely maintain a presence here,” said Sara Shaw, 24, an Occupy movement organizer from California who has lived in McPherson Square since October. She estimated there were 100 people left in the encampment. “It’s less than if you compare it to the beautiful fall, but that doesn’t mean people don’t still support us,” she said. “I plan to come back every day.”

Some park inhabitants seemed to be focused on their own plight — not yet packing up their sleeping bags but mentally preparing for eviction. Several said they had no place to go and no plans.

“Here I feel like I’ve found a family for the first time in my life. If they make us leave, it will be like breaking that family up,” said Sarah Anderson, 29, of Alexandria, who has been living for weeks in a white tent under a magnolia tree, along with a 9-month-old cat named Jinx.

“We have had a lot of thoughtful conversations the past few nights about what to do next,” she said.

Although a bit bedraggled from the recent rain, the camp has assumed an organized routine. A young man wearing headphones went among the tents Saturday collecting trash. Servers ladled out macaroni and hamburger stew to people with paper plates. A sign explaining hypothermia symptoms and precautions was on a tent with medical supplies inside.

The tent colony has evolved into a mini-neighborhood over the months.

Some tents had makeshift porches with armchairs, flags on bamboo poles and cable spools used as tables. Some campers have placed tents within tents for warmth, and even pet igloos are being used as sleeping cocoons.

Many occupants have made their tents into manifestoes, covered with political slogans and philosophical quotes. But on Saturday, yellow fliers had also been taped or pinned to every tent, courtesy of the Park Service, with a list of rules.

“I came here to absorb some energy, but I don’t feel very much,” said a middle-aged tourist from Missouri, “Everyone just seems sort of tired.”

But that evening, protesters perked up, chanting, drumming and pressing close to barricades around the Capital Hilton, where Obama was at the annual Alfalfa Club dinner. A man held up a sign that read, “I NEED WORK NOW! Please HELP?”

Referring to formally clad club guests, Ethan Miller, 20, an American University student from Rockville, said: “We want to send a message that these people are living off the backs of others and flaunting their wealth. . . . We came to tell them that’s not okay to be exploiting others.”

As prominent Washington figures in tuxedos and gowns began emerging around 11 p.m., some behind a protective screen of police officers, protesters were still there to jeer and heckle.

Staff writers Susan Svrluga and Clarence Williams contributed to this report.