The search for silver, which daily grows more precious, has taken some men beyond the pale of unplumbed mountainsides into the darkened closets of Maryland hospitals.

The prize: stored x-ray film.

Because those shots of fractured kneecaps and cracked femurs, as well as unexposed film, contain silver bromide, hospitals have become the target of thieves who resell the plates to metal salvagers for $6.50 a pound.

Last month the Maryland Hospital Association warned its 62 member hospitals to tighten security after two men posing as employes of a silver salvage company walked out with 4,600 pounds of superannuated x-rays. The haul, at November's prices, was worth $11,500.

Another hospital on the Eastern Shore was hit and last weekend University of Maryland Hospital in Baltimore lost $1,800 in unexposed film.

Either by burning or a washing process, one pound of x-rays will yield about one-eighth of an ounce of silver. Depending on the kind and size of plates, it takes 15 to 20 chest x-rays-size plates to make one pound.

"When silver was $5 an ounce we were paying 85 cents for it," recalled Charles Narron, president of a salvage firm that buys film from many Maryland hospitals. As the price for silver is nearing $40 an ounce, the x-ray film has jumped to $6.50 a pound.

"Our average load is 10,000 to 12,000 pounds," Narron said. "You're talking about a lot of money.'

In Baltimore, a number of hospitals have received "suspicious calls" from people who offer to purchase x-ray film.

"The callers say, 'We'll come in and pick up old x-rays and we'll pay cash'," said hospital association spokesman Richard Wade.

Baltimore police say the scam is the work of a single band of "gypsies" who offer to buy a few hundred pounds of the hospital's x-ray plates to make silver trinkets, but use the occasion to familiarize themselves with the location of the x-ray storage area.

In the Washington suburbs, hospitals spokesman reported no x-ray thefts as of yesterday, but said they are beefing up security.

"It's a concern," said Tom Burke, spokesman for Holy Cross Hospital in Silver Spring. "There's a problem in the area."

A few hospitals actually do their own silver salvaging.

At Montgomery General Hospital inOlney, the radiology department goes through more than 10 cases of x-ray film a week, which can cost up to $700 per case. The hospital retrieves its own silver through a washing and electrolysis process.

"The price of x-ray film has gone up 50 percent in the last quarter," said Donald Kreitlow, head of x-ray technician at the hospital. Montgomery General recovers more than one pound of silver every week from used film.

"We got ripped off a year ago," Kreitlow said. "Security's been tightened up pretty good."

Hospital spokesman Richard Wade said yesterday that the theft of x-rays was "a product of the times."

As with many things, however, they don't make x-ray film like they used to. Before 1976, there were 23 to 24 ounces of silver in 100 pounds of Eastman Kodak film.Now the film contains 11 to 15 ounces per 100 pounds and the Polaroid Corporation is working on a product that will use even less silver.

But, says, Kreitlow, there will always be silver lining in x-ray film.

Meanwhile, police are still looking for the x-ray thieves, aided by the fact that there are few places to fence 4,000 pounds of x-ray film.