As a professional firefighter for the last 25 years, I take extreme exception to your editorial ''Prince George's Sprinkler Law'' {Nov. 21}. After the recent tragic loss of six lives and the near-total destruction of a single-family home in Prince George's County on Nov. 26, maybe The Post will change its opinion and not only support the sprinkler law for Prince George's, but also support such a law for the entire metropolitan area.

The National Fire Protection Association reports that nearly three-fourths of all deaths and injuries caused by fire in the United States occur in one- and two-family dwellings. Your editorial states, ''About 137 Prince George's County residents have died in fires in the past decade, two-thirds of them in single-family houses.'' You continue: ''This law will save lives, and that's worth the cost of placing sprinkler systems in high-rise apartments or the garden apartment variety of large multifamily dwellings. Making sprinkler systems mandatory for every new single-family home, however, is excessive. It could provide more headache than safety.'' It would appear that your statement is a contradiction to the NFPA statistics and that this new sprinkler law would result in more lives being saved from fires in single-family homes than in multiple-type occupancies.

You also state that many home burglar alarms and smoke alarms go off by accident and that maybe the sprinkler systems will malfunction and cause water damage. However, if you check with the NFPA, any local fire department officials or the owner and occupant of any building where sprinkler systems are properly installed, you will find that the accidental discharge of water from an automatic sprinkler system is very, very rare.

Please, to save lives and prevent injuries to civilians caused by fire in any type of dwelling and also to save firefighters from death and injury, support the sprinkler law. Then someday newspaper headlines will read: ''There Were No Fire Deaths or Injuries and Very Minimal Damage From a Fire in a Single-Family Home Thanks to an Automatic Sprinkler System.''

-- James E. Gallagher The writer is a battalion fire chief of the District of Columbia Fire Department.

The Post stated that the sprinkler heads go off at a temperature "considerably lower . . . than it takes to boil an egg." That sentence really fried me. It only served to demonstrate the writer's lack of understanding of residential sprinkler systems.

The fire problem in the United States is a serious one, and residential sprinklers are proven life-savers. From 1977 through 1984, an average of 6,633 civilians died each year from fires nationwide.

Residential sprinklers are a cost-effective way of combating fire. On average, the cost of an installed residential sprinkler system is less than 1 percent of the total cost of the house. After the installation, you can begin to subtract the money saved on insurance premiums from the initial outlay.

The failure rate of sprinkler heads in commercial applications is known to be less than one per million heads installed. It is also known that it is easier to dry out one's possessions than it is to "un-burn" them.

The editorial states that 137 Prince George's residents have lost their lives to fire in the last decade, two-thirds of them in single-family homes. Why then did the editorial support the use of sprinklers in apartment buildings and not in single-family homes? The single-family home is where the fire death statistics are greatest. The single-family home is also the one place in the United States where the fire department has the least jurisdiction.

It is only through strong, effective building codes, such as Prince George's new sprinkler law, that the fire department can "get into" the private home and prevent fires from becoming deadly.

I recommend that The Post stick to boiling eggs and leave fire-safety legislation to the experts. -- John W. Banks III The writer is deputy fire chief of Gaithersburg-Washington Grove Fire Department, Inc.