HAMPSTEAD, N.C. (AP) _ U.S. Marines today replaced tired volunteers on lines around a smoldering fire that has charred 73,000 acres of peat-rich forest in eastern North Carolina since it began 10 days ago.

''The flashy work is over,'' said Donald Kass, a spokesman for the state forest service. ''Now begins the drudgery.''

Twenty-one volunteer fire department units had fought the blaze in Pender County and a portion of Onslow County since May 5. The Marines were asked to replace the volunteers to keep the manpower at about 200, Kass said. There are about 150 forest service workers from around the state on the scene.

A lot of rain is needed before firefighters can rest easy, said fire boss Tommy Thompson. Forecasters said there was a chance of thundershowers today.

''It looks real good,'' Thompson said. ''The lines have held ... but as long as there's a ground fire and a chance it could get out of the line ... we're not going to call it contained as long as it's a threat to the life and property of Pender and Onslow counties. For the near future, we're going to be doing a major reinforcement of the fire line, then going in to mop up the hot spots.''

Thompson said firefighters were not able to get all of the Marine Corps equipment they had hoped to use. He said they would get three M-50 1,000- gallon water pumps and 20 additional Marines. They already have two P-19 crash trucks to spray foam on the fire and three more pump units with about 25 Marines.

All but about 4,000 acres of the 48,500-acre Holly Shelter Game Management Area in Pender County were burned, and officials planned to take a helicopter tour today to assess damage to wildlife, said George Smith of the state Division of Wildlife Management.

''We're going to try to get a handle on what the losses might be, what the survival might be, to see if there are any injured animals. We're going to check out the habitat and get prospects for recovering to see if it can support the critters that survived,'' Smith said.

On Wednesday, firefighters, aided by low winds, high humidity and an occasional sprinkle, finished plowing fire lines around the blaze.

''We're going to win,'' said John Lively, division chief at the northernmost extension of the fire about four miles south of Maple Hill. ''With a break from the gods, we'll make it today.''

Firefighters battling the 14-mile-long fire had it 98 percent contained earlier Wednesday, Thompson said. Lively's crews helped finish the final lines needed to complete the 44-mile perimeter early Wednesday night.

Huge bulldozers plowed lines through 50 acres of smoldering debris on an International Paper Co. tree plantation that had been burning for three days. Crash wagons sprayed foam normally used for burning airplanes on pines standing in smoking peat.

At another front-line hot spot, Richard Vinson of the North Carolina Air National Guard supervised 10 men cooling down smoldering areas and reinforcing fire lines.

''This peat is a strange animal,'' he said. ''You think the fire's gone, then you wait 20 or 30 minutes and look over several hundred feet and see it pop out again.''

Around the rest of the fire's perimeter, about 150 state Forest Service firemen and volunteers from fire departments around the state were improving lines to hold against changing winds or falling humidity, Thompson said.

Forecasters said there was a chance of thundershowers today. Firefighters have said it will take drought-breaking rains of 2 to 3 inches to declare the fire out.

Don Kaas, a spokesman for the state Forest Service, said Wednesday the long battle against the fire has cost the state at least $308,000, not including some aircraft costs and the expenses of volunteer fire departments.

Damages to private woodlands and a state game preserve have not yet been appraised, he said.

Meanwhile, forest resources officials Wednesday lifted burning bans in 23 western counties because of light rain that began falling Tuesday. Burning bans are still in force for 41 Piedmont and coastal counties.