Trying to fill vacancies and cut overtime costs, the D.C. Fire Department has shortened its customary 10-week training course for recruits to six days, a move some veteran firefighters say will hamper the overall proficiency of the department.

Department officials said 14 new firefighters who graduated June 17 from the department's "crash course" have been assigned to fire companies around the city. About 50 more will graduate and begin working by Sept. 1, the officials said.

Fire Chief Norman Richardson said yesterday that the decision to cut back the training program was a "purely financial one." The department pays more than $4,200 in day in overtime to fill the 25 vacancies in the 1,400-member force, and officials say 81 more positions will open up through retirements by Sept. 1.

Pointing to the more than $2.5 million in budget cuts the department has suffered over the past year, Richardson said the department "has to fill the positions and cut down on overtime to be solvent for the rest of fiscal year 1980."

Richardson said that by October, when fiscal year 1981 begins, "we will be on firmer financial ground and will be able to give the trainees the remainder" of their 50-day session. That includes 81 hours of emergency medical technician training.

D.C. Firefighters Association president Bill Hoyle said he was not "real crazy about" the change, "but in times of financial crisis they have to do certain things, and this is one of them."

Deputy Chief Theodore R. Coleman, head of the department's training division, said he didn't believe the new firefighters would be a "handicap" to the department. However, he acknowledged, if the firefighters had gone through the full training course "they could be treated almost the same as a veteran when he got out on the street . . . As it is, there are certain things they just can't be assigned to do because they didn't get any training in those areas." Coleman said first aid was one of those areas.

To make up for their lack of training, Coleman said, rookie firefighters are closely supervised by officers and veterans at the scene of a fire. The recruits, he said, "are never left alone . . . Their actions and progress are constantly monitored by officers. They are still being trained. It just isn't in the classroom. It's good practical experience for them to go on runs early in their career."

Chief Richardson said it has been only in the last 10 years that recruits received any training before being assigned firefighting duties. Prior to that, firefighters often went through two to five years of direct firefighting experience before undergoing any formal training, he said.

But one veteran fireman said yesterday that firefighting " is a very involved team effort. . . . If one guy isn't pulling his weight, everyone's in danger because they have to compensate for him. . . . We're trying to help these guys out, but you can't help but wonder if they'll be able to come through when you need them."

"There's no question it could be a danger," said Lt. William Andrews, who is stationed at Truck 8 in far southeast.

The rookies, he said, are "not anywhere near as well qualified as people who have taken the full course . . . It's tough on them.

"They have had to absorb so much information at one time, it's hard to grasp it all. We're trying to give them all the things they need to know right now. . . . Everybody's trying to tell them what to do at the same time, and that's not the best procedure. You can't give them too much and overwhelm them either. They get confused."

Rookie firefighter Alfred Jeffery, 22, a former construction worker, said yesterday that even though he had been a volunteer firefighter in Prince George's County, "when they told me they were shortening our 10-week course down to six days, I was sort of scared."

Though Jeffery said he has not yet been involved in a major fire -- none of six rookies interviewed yesterday had -- he said "everybody's been pretty helpful. . . . I feel basically confident. After a while you learn that all fires, no matter where they are, are hot."