They are the white-gloved sentries, standing guard at New York City’s better addresses, so signature a feature of life here that we tend to forget that in other metropolitan centers like Paris, London, Chicago or Boston uniformed doormen (and, less often, women) barely exist.

They form a small army, some 35,000 residential doormen, concierges, porters, handymen and supers represented by a powerful union, 32BJ. They open doors, of course, load cars, receive packages, pass dogs off to professional walkers and in general make themselves indispensable to an ease of life many in this demanding town take for granted.

Yet as protectors of the border between public and private, doormen play a role crucial to the currents of the metropolis, one never more evident than now when the front line of a global pandemic is one’s threshold.

“Yes, it’s a job, but we also try to keep the building as a home,” said Alberto Ventura, 65, who has worked the door at the same Park Avenue building for 42 years. “With the virus, we’re trying to take it a day at a time and be as calm as we can.”

Reassuring staidness has long been a selling point at doorman buildings like those that flank Park Avenue, with its long stretch of level cornice lines, as well as at the august edifices ornamenting Fifth Avenue, Central Park South and Central Park West.

In places like these, where the buildings have names that seem filched from Thomas Hardy or street numbers that send the blood of real estate agents racing, the inescapable tumult of city life is stops at windowed wooden bi-fold doors, inset with ornamental iron grilles.

Once past the mahogany portals, residents and visitors alike experience an almost sedative calm and a security induced in large part by the assembled elements of a universalized department-store version of taste.

Almost inevitably there are marble floors with truffle insets, acres of Persian carpets, hard-backed settees upholstered in maroon leather, silk-shaded ginger-jar table lamps casting light on phalaenopsis orchids planted in generic tole jardinières.

These days, of course, every surface, no matter how perfected, has become a potential site of danger, and it has become the job of Mr. Ventura and others in his line of work not just to swab elevator buttons with Lysol five times daily, but also to restore the psychic equilibrium of those to whom bad things are not supposed to happen.

At increased risk to themselves, the staffs at most high-end buildings throughout the five boroughs find themselves scrambling to institute hygienic measures. They are also enforcing daily changing guidelines, establishing ad hoc networks of notification, caring for the old and vulnerable left behind by an exodus that has rendered the Upper East Side a ghost town.

“We’re not a hazmat crew but we’re doing what we can,” Jimmy Brennan, 40, the resident manager of a cooperative building on Fifth Avenue, said of his nine-member team. “The trick here is anticipating the needs and problems before they come up.”

At Mr. Brennan’s building in the East 70s, that meant appealing to his board of directors — well before the Centers for Disease Control and Prevention issued stringent updated safety guidelines — for a go-ahead to shut down the gym and common areas, to suspend nonemergency contractors, to seal off floors left vacant by tenants who fled the city and to establish a phone tree and daily wellness check-ins with those that remained.

“Our population is mostly aged 60 to 100, 85 is a pretty common number here,” said Mr. Brennan, a third-generation building manager whose extended family oversees 30 separate buildings around New York. “History will judge whether it was better for us to be proactive than reactive. But, for now, I’d rather be effective than popular.”

There is a conundrum in all this, one not lost on Mr. Brennan. As guards at the front lines of a highly communicable virus, the doormen and porters at his building safeguard tenants by exposing themselves. “There is no choice, really,” he said. “That’s the job.”

Although workers united under the banner of the union earn good wages, few can afford to live in Manhattan, let alone escape to the putative security of a weekend refuge.

“It’s scary and I’m nervous,” said Frankie Echevarria, 45, a longtime doorman at the Lafayette, a 146-apartment cooperative on East 9th Street in the Village.

“I keep my distance, but I try to stay positive,” he added, noting good-naturedly that it was with some reluctance that he has begun policing for new coop rules banning open houses; food deliveries past the front desk; or tenants congregating in common areas. “People think New Yorkers are hard-core and tough. But, really, we’re just pussycats.”

Naturally, Mr. Echevarria said, he routinely dons latex gloves and lavishly deploys the building’s stock of Clorox to deter cross-contamination. Yet exposure to the coronavirus continues to hold added terror for him, he said, since his wife suffers from a serious immune disorder. “At the end of the day, though, we’re here to help,” Mr. Echevarria said.

The Lafayette, a large building with an activist board, was quick to compile a phone tree so volunteers could assist the staff in aiding the homebound. Its longtime resident manager, Jay Miranda, 48, said it’s “a nice little community here.”

Still, there may be few among the 300 residents of the building who could easily come up with the doormen’s surnames, which appear once a year on an annual staff list produced by the board of directors at Christmas and may be forgotten as soon as tip envelopes are addressed.

“It’s easy to undervalue them,” said Adam Soffer, a private mortgage banker at Wells Fargo. Symphony House, where Mr. Soffer lives, was designed by the architects Emory Roth & Sons and is considered among Manhattan’s premier addresses.

“But if ever there were a time to overvalue them, it’s now,” said Mr. Soffer, who recently had takeout dinners delivered to his building’s night crew. “These guys are on the front lines for the rest of us.”

Alarmingly, those front lines refuse to stay fixed, said Rudy Mercado, 40, the resident manager at a 39 story cooperative on the Upper East Side. Back in February, Mr. Mercado requested funds from his board of directors to buy surgical masks for doormen, valets and porters, air filters for elevators and clear plastic sheeting to cover call buttons.

When it was reported that the virus can survive on inert surfaces like cardboard and plastic, he went back to them for money to install an Ozonator tent for packages. “Normally, we get about 60 a day,” Mr. Mercado said. The number quadrupled once people began to shelter indoors. “Now it’s like Christmas,” Mr. Mercado said.

“I don’t know that it would help,” he added, of the tent, which helps disinfect the packages. “But I can’t imagine it would hurt.”

Managers, doormen and valets, with their quiddities and quirks, help set the tone for the singular ecosystem that is any given apartment building, as Mr. Soffer, the banker, explained. The relationship between them and residents, as with concierges in Paris, is an unusual combination of familiarity and distance, formality and — during moments like this — tenderness.

“There’s the young guy that’s quiet, and the older guy that’s a grump,” Mr. Soffer said. “The building has always been run like the Starship Enterprise, but until this happened and I stopped to listen to them, I never realized how at risk these guys were, even from the viewpoint of living paycheck to paycheck.”

Like so many of those responsible for keeping New York running, its doormen are both omnipresent and yet oddly unseen. Last week, as all New Yorkers began to shrink from human contact and hunker down in self-isolation, their presence in their woolen greatcoats, piped trousers, neckties, white shirts and white gloves, lent the city a needful element of stability.

“We’re in this moment where no one will touch anyone, and cashiers won’t take credit cards and you don’t want people breathing on you and these guys are still there on the front lines,” Mr. Soffer said. “They don’t have the option to go the Hamptons — they have to touch. Just thinking about all that gave me a new level of appreciation and respect.”