Gun manufacturers and enthusiasts, led by the National Rifle Association, have spent more than $5 million so far in their effort to defeat a landmark California gun-control initiative, close to a record for spending on a statewide ballot measure.

The massive television, radio and newspaper campaign has dwarfed the $1.7 million spent so far on behalf of the proposal, called Proposition 15, which would put a ceiling on the number of handguns in the state and require their registration.

The latest California poll by Mervyn Field shows the measure that is on next Tuesday's ballot losing for the first time, 49 to 41 percent.

Both gun-control supporters and opponents say the results in California may influence nationwide efforts to curb handguns for years to come.

The huge anti-15 campaign chest "allowed them to get their ads on the air at least one and one half months before we could do anything," Howard Gingold, press secretary to the "Yes on 15" campaign, said. "That made a big difference."

California is one of 18 states where citizen petitions have placed a total of 51 initiatives on ballots this year. It is the largest number since 1932.

But as often happens, the California initiatives are among the most controversial and expensive.

According to records filed with the California secretary of state as of Oct. 16, the "No on 15" campaign is not even the highest-spending initiative effort here this year: a total of $5.2 million has been spent, mostly by grocery and beverage industry groups, in the campaign against a measure similar to that already in effect in six states requiring at least a 5-cent deposit on each beverage container.

The record for spending on a state ballot proposition is $7.1 million, set here in 1978 when an initiative to limit smoking in public places was defeated.

Californians have never voted statewide on a gun-control measure, and the proposal before them is unique.

It would put a ceiling on the number of handguns, now estimated at between 3.2 million and 5 million in the state, ban the importation of handguns after Election Day, and prohibit the sale of unregistered handguns after April 30.

Residents could still buy registered guns from dealers or each other, a concession to citizens worried about protection of their homes that makes the initiative different from the strict District of Columbia gun-control act.

Supporters argue the initiative would reduce handgun crime and accidents, and give police an additional tool to stop criminals by establishing a mandatory six-month jail term for carrying a concealed handgun in public.

Opponents argue that the initiative would limit citizens' ability to protect themselves and not really deter crime.

The NRA has contributed $2.8 million, more than half the total for the anti-15 campaign. Most of that has come from direct mail appeals to NRA members, according to NRA media relations director Paul C. Stone, who is based in California temporarily to help the campaign effort. He said average contribution was about $21.

The television commercials in support of the initiative have relied heavily on emotional appeals from the relatives of handgun victims, arguing that the proposition would be worth the trouble if it saved just a single life. Among those making the television appeals are San Diego voter and former hostage in Iran, Richard Morefield, and his wife Dorothea.

The Morefields' son, Richard Jr., 19, was one of four people killed by a man with a .32-cal. revolver in the 1976 holdup of a Roy Rogers restaurant in Annandale, Va.

While gathering 580,000 signatures in less than four months to put the proposition on the ballot, gun-control supporters also registered several thousand new voters, particularly in university communities like Berkeley.

"No on 15" billboards have been plastered around the state and opponents have aired in several cities an effective, 28-minute television documentary narrated by Charlton Heston which raises doubts about the effectiveness of gun-control measures in other states.

But major stations here and in San Francisco have declined to show it because of its length.