By Alex Dobuzinskis

(Reuters) - San Francisco's Golden Gate Bridge marked a milestone in 2013 as 46 people leaped to their deaths in what appears to be the deadliest year for suicides at the California landmark, a watchdog group said on Tuesday.

The Bridge Rail Foundation, which tracks fatalities at the 4,200-foot-long (1,280-meter) span, said the high number of suicides demonstrates the need for a safety net to be installed to make it more difficult for would-be jumpers to take their own lives there.

"I know it won't be built soon, and that's the most frustrating thing about this," said Dayna Whitmer, board member with the organization. "We hate to see any more 17-year-olds jump or 86-year-olds jump, it's just not right."

The road surface of the suspension bridge towers more than 220 feet above the entrance to the San Francisco Bay, and the span ranks as one of the world's most frequently chosen sites for public suicides. It is also one of the most lethal, with jumps from the bridge nearly always proving fatal.

A spokeswoman for the Golden Gate Bridge Highway and Transportation District, Mary Currie, confirmed that 46 people had committed suicide at the bridge last year, the highest annual total since at least 2000, when she began keeping an unofficial count.

Currie said police officers or others had intervened to stop another 118 people from leaping off the span in 2013.

Whitmer said last year's suicide tally, up from 33 in 2012, was the "highest we can confirm" since the bridge was built in 1937, adding that the previous record was believed to be 40 or 41 in a single year. An analysis published by the San Francisco Chronicle found 40 suicides occurred at the Golden Gate in 1977.

Officials have drawn up plans to install a safety net beneath the span's sidewalks to catch people who jump but are still seeking the estimated $66 million needed to construct it. In 2011, a firm was given $5 million to design the net, Currie said.

Story continues

For now, officials work to prevent suicides with law enforcement officers on bicycle patrols. At any given time, two to four officers are on the bridge's sidewalks, said California Highway Patrol spokesman Andrew Barclay.

Authorities have offered no explanation for the high number of suicide jumpers last year.

"Suicides really come in waves, it seems like some years are high, some years are low," Barclay said, adding that during the economic downturn officers frequently encountered suicidal business owners or people losing their homes.

The total number of people who have jumped to their death from the bridge over the years is unknown, largely because of spotty recordkeeping and because the bodies of some who jump are never recovered, Whitmer said.

Whitmer's own 20-year-old son, Matthew, is believed to have committed suicide at the Golden Gate in 2007 after he was reported missing and the car he drove was discovered near the bridge, she said.

She said a safety net would cut down on future fatalities by saving individuals from what is often an impulsive decision.

"If we can give them the time to get through that crisis, then they can go back and get help or call someone," she said.

(This version of the story corrects reference to California Highway Patrol spokesman in the 9th paragraph)

(Reporting by Alex Dobuzinskis; Editing by Steve Gorman and Ken Wills)