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Homeless women near Skid Row in Los Angeles, preparing for another night on the streets.Credit Frederic J. Brown/Agence France-Presse — Getty Images

LOS ANGELES — Flooded with homeless encampments from its freeway underpasses to the chic sidewalks of Venice Beach, municipal officials here declared a public emergency on Tuesday, making Los Angeles the first city in the nation to take such a drastic step in response to its mounting problem with street dwellers.

The move stems partly from compassion, and in no small part from the rising tide of complaints about the homeless and the public nuisance they create. National experts on homelessness say Los Angeles has had a severe and persistent problem with people living on the streets rather than in shelters — the official estimate is 26,000. The mayor and City Council have pledged a sizable and coordinated response, proposing Tuesday to spend at least $100 million in the next year on housing and other services. They plan, among other things, to increase the length of time shelters are open and provide more rent subsidies to street people and those in shelters.

“Every single day we come to work, we see folks lying on this grass, a symbol of our city’s intense crisis,” Mayor Eric Garcetti said at a news conference at City Hall on Tuesday. “This city has pushed this problem from neighborhood to neighborhood for too long, from bureaucracy to bureaucracy.”

In urban areas, including New York, Washington and San Francisco, rising housing costs and an uneven economic recovery have helped fuel a rise in homelessness. In some cities, officials have focused much of their efforts on enforcement policies to keep people from living in public spaces.

In places known for good weather like Honolulu and Tucson, or for liberal politics — like Madison, Wis. — frustration has prompted crackdowns on large encampments. Some cities, like Seattle, have tried setting aside designated areas for homeless encampments. But to date, no city has claimed to have the perfect solution.

Like other urban mayors, Mr. Garcetti has made promises to end chronic homelessness. Yet the homeless population here has grown about 12 percent since he took office in 2013. He, too, has been criticized for taking a heavy-handed approach to enforcement while doing too little to help people find and pay for housing. City budget officials estimate that Los Angeles already spends more than $100 million, mostly through law enforcement, to deal with issues that stem from people living on the streets.

In New York, Mayor Bill de Blasio has been grappling with a soaring homeless population since he took office nearly two years ago. The number of people occupying homeless shelters peaked around 60,000 last winter and remained stubbornly high — around 57,000 — this week.

Unlike the dispossessed in Los Angeles, the vast majority of the homeless in New York are sheltered. But the presence of the street homeless, highlighted on the front pages of tabloids, has put public pressure on Mr. de Blasio to address the 3,000 unsheltered homeless holding signs on sidewalks, sleeping atop subway grates and huddling in encampments.

Increasingly, young families are becoming the most potent symbol of homelessness, with mothers who work multiple jobs living in shelters in New York or in their cars in Los Angeles.

“This is the fallout of not having anywhere near the affordable housing that’s needed,” said Megan Hustings, the interim director of the National Coalition for the Homeless, a Washington-based advocacy group.

“It is repeated all over the country: We work to get them emergency food and shelter, but housing continues to be unaffordable, so you see people lingering in emergency services or going to the streets.”

In Los Angeles, rents have soared all over the city and housing vouchers usually cover only a fraction of the rent for a home near public transportation. Efforts to build new housing units have floundered, and the city’s spending on affordable housing has plummeted to $26 million, roughly a quarter of what it was a decade ago.

Neighborhoods that were once considered hubs of relatively inexpensive motels and single-room apartments — Venice Beach, the Downtown Arts District — have been transformed into well-to-do enclaves filled with cupcake emporiums and doggy day care centers.

A census of the homeless in Los Angeles County released in May found that the number of people bedding down in tents, cars and makeshift encampments had grown to 9,535, nearly double the number from two years earlier. More than half of the estimated 44,000 homeless in Los Angeles County live in the city limits, according to the census. And nearly 13,000 in Los Angeles County become homeless each month, according to a recent report from the Economic Roundtable.

The spending proposal will need to be approved by the City Council and allocated by its Homelessness and Poverty Committee. The $100 million figure was chosen in part for its symbolism, said Herb J. Wesson Jr., the City Council president, to show county, state and federal officials that the city was willing to make a significant contribution to an urgent problem. “Today, we step away from the insanity of doing the same thing and hoping for different results, and instead chart our way to ending homelessness,” he said.

But many longtime advocates for the homeless here said the City Council’s proposal was not likely to make a big dent in the number of people who are finding themselves on the streets. “Encampments used to be contained to Skid Row, where city officials would try to control or ignore them,” said Gary Blasi, a law professor at the University of California, Los Angeles, who has studied homelessness in the region for years. “Plans have been made, and never made it off the paper they’re written on. It’s not clear what will be delivered. And do the math here — it doesn’t amount to much at all.”

In New York, Mr. Blasi said that hundreds of existing housing vouchers went unused because homeless people could not find landlords who would accept them.

While overall homelessness has declined nationally, urban areas with rising rents are facing the most acute problems.

“People who would have thought of themselves as homeowners 10 or 15 years ago are renting, and it’s a grim situation in a lot of places,” said Steve Berg, the vice president for programs and policy for the National Alliance to End Homelessness. “A lot of places don’t have a real grip of what the homeless population is in real time, and respond only crisis to crisis. But what we’ve learned about homelessness over many, many years is that you have to provide housing, and criminalizing the homeless doesn’t keep people off the streets at all.”

Earlier this year, the Los Angeles City Council approved an ordinance that lets the police confiscate property and makes it easier for them to clear sidewalks of homeless encampments. Similar legislation has been passed in other cities.

In Honolulu, where the city has spent the last two days shutting down homeless encampments that have irritated residents and frightened tourists, a federal judge on Tuesday denied the American Civil Liberties Union’s request to stop seizing and destroying people’s property during the sweeps.

Mr. Garcetti proposed using $12.6 million this year from unexpected tax revenue for rental subsidies for short-term housing and other services, including $1 million to create centers where the homeless could store belongings and shower. The $100 million, if approved, would be for the 2016 budget.

Some advocates for the homeless here have said that the rising street population has created a public health crisis on Skid Row downtown, where about 5,000 people now live outdoors.

“It’s a humanitarian crisis and a moral shame,” said José Huizar, a council member who represents the area. “It has reached a critical breaking point, that the sea of despair that we witness on the streets of Los Angeles each and every day must end, and it begins with all of us here today.”