A fight between city and federal officials in Alexandria is threatening to do what snow, rain, heat and gloom of night have rarely done: halt the U.S. Postal Service in its tracks.

For the past six months, Alexandria building officials have written letters to the Postal Service demanding it install a sprinkler system in the city's new post office, under construction at 610 N. Henry St.

The Postal Service has refused, saying that federal buildings such as the post office are exempt from city regulations.

"We, in the federal government, have a higher responsibility and therefore are not permitted to defer our judgment and responsibility to local or state officials," George A. Tedesco, a regional postal construction program manager in Philadelphia, told city officials in a recent letter.

That attitude has only made Alexandria officials redouble their efforts to bring the $2 million building into compliance with the city's building codes. If the Postal Service persists, the Alexandria officials said last week, the city will deny water and sewer service and underground electricity permits to the new building.

And that, the city officials said, should stop the mail. The new post office, which will replace the Old Town post office at 200 S. Washington St., is scheduled to be finished in November. Assuming the impasse remains, Uwe K. Hinz, Alexandria's top building official, said: "There will come a time when they'll be delayed."

Thus far, Hinz's appeals have been rejected. "The life safety of your employes and patrons continues to be ignored and it also seems apparent that you have little respect or regard for local firefighters that would respond to a fire emergency at your new facility," Hinz told Tedesco in one of the letters.

Tedesco contends that the Postal Service did voluntarily agree to meet Alexandria's building codes. "We've satisfied our own requirement and local codes regarding exiting requirements during a fire emergency." he said.

Specifically the Postal Service is at odds with Alexandria over whether certain areas of the new post office should be designated as "work areas" which require sprinklers. The city says that the building contains such areas; the Postal Service says no; the rooms are "in fact places of general business" and sprinklers are not required.

Moreover, notes Tedesco, "We don't sprinkle buildings under 25,000 square feet." Installation of a sprinkler system in the one-story, 17,000-square-foot post office would cost a minimum of $30,000, he says.

Tedesco consulted with officials at Postal Service headquarters at L'Enfant Plaza after Alexandria officials complained.

But headquarters may have been the wrong place to ask.

Last October's spectacular fire there, described as one of the largest ever fought in the District, caused an estimated $100 million in damage and spread quickly because the building lacked a sprinkler system, D.C. fire officials said.

Hinz says he is baffled by the dispute. "We have required sprinklers in buildings that are used in a similar nature, such as United Parcel Service. The people that have developed office buildings in Alexandria have been extremely helpful in meeting building codes . Why the post office refuses escapes my rationale."

The sprinkler showdown is not the first controversy to surround the new post office. In July 1984, when plans for the contemporary-styled building were submitted to architecture-conscious Alexan- drians, then-Mayor Charles E. Beatley suggested that the building would look "like a mortuary or a graveyard."

And then-City Manager Douglas Harman did not help matters when he said: "I'm sure people would drive by there and wonder who's buried behind those walls."

That time the federal government bowed to the objections and replaced the brick and precast concrete archways that would have enclosed two exterior courtyards in the front of the building with a brick planter and a wrought iron fence.