NEWARK, N.J. (AP) _ The world's first dual-chamber pacemaker to use nuclear power was implanted in the chest of a 47-year-old man this week, and doctors said the atomic energy source will help the device last as long as 40 years.

''Theoretically, this pacemaker will last a lifetime,'' said Dr. Victor Parsonnet, who operated on John Sniffen of Clifton on Tuesday at Beth Israel Medical Center here.

Pacemakers, which regulate the heartbeat, have been around for years, but the device given to Sniffen is the first dual-chambered design powered by plutonium. While conventional battery-powered pacemakers must be replaced every five to eight years, Sniffen's is expected to last from 20 to 40 years.

Single-chamber nuclear pacemakers exist and last about 16 years, but the two-chamber design more naturally maintains the human heart's two-step rhythm. When the heart beats, the lower part squeezes blood into the upper chamber, where a second squeeze then sends the blood into the rest of the body.

The Pulsar-N1 pacemaker, an oblong device about 2 1/2 inches wide and an inch thick, is placed between the skin and the muscle of the chest wall.

Two wires are threaded through a vein to the heart, where they are attached to the upper and lower chambers, alternately jolting them with electrical impulses and adapting to the patient's rate of activity, Parsonnet explained at a news conference Thursday.

Single-chamber pacemakers only stimulate the lower chamber, said Parsonnet, who helped implant the first U.S.-made, single-chamber, nuclear-powered pacemaker in 1973.

Doctors developed a dual-chamber pacemaker in 1974, but the power source was a lithium battery that has a lifetime of five to eight years.

Nuclear pacemakers, powered by plutonium 238 encased in titanium, do not emit harmful levels of radiation, doctors said.

''Of the 3,000 to 4,000 put in worldwide there's never been any evidence of the isotope plutonium doing any harm to the patient or the environment,'' Parsonnet said.

''The average abdominal X-ray dose is about twice what you would get from the nuclear pacers,'' said David L. Purdy, president of Biocontrol Technology, the Indiana, Pa., company that manufactures the device.

Sniffen, who was listed in good condition, told reporters the single- chamber, nuclear-powered pacemaker he received in 1975 gave him ''jolts every once in a while and (I) was totally aware of it.

''Now I feel good. A little weak from the operation, but other than that, it's real nice,'' he said.

A photocopying and facsimile machine salesman, Sniffen suffers from intermittent heart block, a condition that makes the heart stop occasionally and can cause the patient to faint.

Parsonnet said that with its greater longevity, the new device can eliminate the need for replacement operations, reducing the physical and emotional stress on the patient and saving money.

But the new pacemaker also has its drawbacks.

Hospitals have to be licensed to implant the nuclear devices and patients have to be registered with the Nuclear Regulatory Commission to use them.

The dual-chamber nuclear device also costs more, about $6,000 compared to for $4,500 for its lithium counterpart. And it is also bigger and weighs more.

''The major issue is the paperwork and the size,'' Purdy said.