Budget belt-tightening threatens to send school librarians the way of the card catalog.

The schools superintendent in Lancaster, Pa., said he had to eliminate 15 of the district’s 20 librarians to save full-day kindergarten classes.

In the Salem-Keizer school district in Oregon, all 48 elementary- and middle-school librarians would lose their jobs under a budget proposal that faces a vote next week.

In Illinois’ School District 90, which spans several rural and suburban communities in the southern part of the state, parent volunteers have been running the libraries in the district’s seven schools since September, in what the schools superintendent, Todd Koehl, described as “a last-ditch effort” to keep them from closing their doors.

And in New York City, where more than half of the secondary schools appear to be in violation of a state regulation requiring them to have a librarian on staff, Mayor Michael R. Bloomberg’s proposed budget calls for laying off 53 of the 365 licensed librarians who remain.

“The dilemma that schools will face is whether to cut a teacher who has been working with kids all day long in a classroom or cut teachers who are working in a support capacity, like librarians,” the city’s chief academic officer, Shael Polakow-Suransky, said.

In New York, as in districts across the country, many school officials said they had little choice but to eliminate librarians, having already reduced administrative staff, frozen wages, shed extracurricularactivities and trimmed spending on supplies. Technological advances are also changing some officials’ view of librarians: As more classrooms are equipped with laptops, tablets or e-readers, Polakow-Suransky noted, students can often do research from their desks that previously might have required a library visit.

“It’s the way of the future,” he said.

Nancy Everhart, president of the American Association of School Librarians, whose membership has fallen to 8,000 from 10,000 in 2006, said that, on the contrary, the Internet age made trained librarians more important, to guide students through the basics of searching and analyzing information they find online.

Libraries, she said, are “the one place that every kid in the school can go to to learn the types of skills that will be expected of them when it’s time to work with an iPad in class.”

Some states, including Arkansas, Indiana and Kentucky, require every public school to employ a certified librarian; others, like Maine, leave staffing decisions to districts. New York requires certified librarians in middle and high schools but not elementary schools, and also requires a certified library assistant for any school that has more than 1,000 students.

But an analysis of state and city data shows there is 1 librarian for every 2,146 students this year, compared with 1 per 1,447 in 2005. At least 386 schools serving students from grades six through 12, or roughly 54 percent of the city’s middle and high schools, do not have a librarian on staff, the records show.

Polakow-Suransky said that once principals received their individual school budgets for the coming year, “we will work with them to ensure compliance with the state’s regulations.” But he noted that some of the schools “need great flexibility to staff them in these tough times.”

Schools around the city have already been flexible: In many elementary schools, classroom teachers are trained to stand in for librarians, and some small high schools that share buildings have pooled their resources to split a librarian’s salary. But there are also libraries sitting unused for lack of someone to staff them.

At a squat brick building in Brooklyn, parents at the elementary and middle schools that share the space banded together a few years ago to improve the library, whose books were so outdated that some still referred to the Soviet Union. They convinced the Brooklyn borough president and the local councilwoman to provide $450,000 for the project. One parent, an interior designer, helped sketch the plans and supervised the renovation.

The new library opened Nov. 17, with nine new desktop computers, an interactive whiteboard and 4,200 titles, but has been used only as a reading space, mostly by kindergarten teachers who bring in their pupils once a week.

“We just put all this money into a project that may never be fully utilized,” said Kiki Dennis, 43, the designer.

The problem is that shortly after the library’s completion, the city announced plans to close the building’s middle school by 2013, prompting a drop in enrollment that officials expect to worsen in the fall. Because school budgets are largely tied to enrollment, the principal decided she could no longer afford to pay half the salary of a librarian, who earns about $70,000. The principal of the elementary school decided she could not pay the salary alone, and so no librarian was hired.

At the Morris High School campus in the Bronx, where five schools — with a total of 1,900 students — share space, the central library has been closed all year because it has no librarian. At the John F. Kennedy High School campus in the Bronx, the lack of a certified librarian was only part of the problem: The principal of one of the six high schools that share the building said the books there were too outdated to be usable.

The principals, with the help of New Visions for Public Schools, which will run two charter schools scheduled to open on the Kennedy campus this fall, submitted a request to Councilman G. Oliver Koppell for $1.8 million to create a media center equipped with e-readers, iPads and a language lab for students not proficient in English. Koppell sought $600,000 for the project in the budget, which must be approved by Thursday. Whether the request will be granted is uncertain.

Polakow-Suransky said he understood that in tight times, principals had to make stark choices — as do their counterparts elsewhere.

Pedro Rivera, the Lancaster superintendent, said that when he realized a few months ago that his largely poor and immigrant district faced a $10 million deficit, he gathered his senior staff members and asked, “If this budget is an expression of our values, what is it that we value the most?”

The team decided to limit class sizes. They made sure there would be no cuts to physical education — “to prevent obesity and promote a healthy lifestyle,” Rivera said — or arts or music. And they protected prekindergarten classes.

Given what was left, he said, “it was either library or kindergarten.”