Three houses were evacuated in the Spring Valley area of upper Northwest Washington yesterday and part of the neighborhood was cordoned off late last night after excavation work unearthed a cache of munitions dating to World War I.

Explosives found in a trench in the 5100 block of 52nd Court NW included four unexploded mortar rounds, as well as three rounds for a 75mm artillery piece, authorities said.

Officials said that the area was secure last night and that the zone in which damage from a blast could occur had been evacuated.

But they also raised the possibility that more munitions might be buried there. They said that they expect to begin disposal of the ordnance this morning and that additional evacuations might be required.

In addition to police and fire officials, military explosives experts and bomb disposal units were called to the site after ordnance first turned up about 1:40 p.m., according to Battalion Chief Theodore O. Holmes, a D.C. fire department spokesman. No injuries or detonations were reported.

The site is in an area where the W.C. & A.N. Miller Development Co. is building luxury houses on what had been one of the largest undeveloped tracts in the city.

The neighborhood, which is also referred to as Westmoreland Heights, lies within a triangle formed by Massachusetts Avenue, Dalecarlia Parkway and Van Ness Street.

A backhoe was digging a trench for a sewer line in front of a recently constructed house when the munitions were discovered.

It was not clear when or why the explosives were buried there, but a spokesman for an Army explosives unit said the spot might have been used years ago as a munitions scrapheap.

"If they did stumble on an old burial site that nobody charted, {there is} no telling how big that site might be," said a spokesman for the Army ordnance disposal team from the Aberdeen Proving Ground in Maryland.

Jim Allingham, spokesman for the Army explosives unit that was flown to Washington by helicopter from Aberdeen, said the four World War I-era mortar rounds found at the site all had fuses in them.

"Any time you've got a fuse in it, you're dealing with a hot potato," Allingham said.

Also found, according to Allingham, was a 105mm round, which was broken, lacked a fuse and was apparently "not operational."

He said the three 75mm rounds also were described as lacking fuses. He said that it was unclear whether those rounds still contained explosives but that even if they did, they were unlikely to detonate without fuses.

Nonexplosive material at the site included equipment for transporting munitions and Livens projectors, which are used for firing munitions similar to mortar rounds, Allingham said. He also said that "the explosives in any of the munitions may have lost their potency with age."

Officials said part of their work today would be to try to reconstruct the history of the site and search for records that might show whether any additional materials are buried there.

Several of the houses in the immediate area of the site were unoccupied. A resident of one of the three that were evacuated because of the munitions discovery said she "didn't like it. . . . When you have to get out of your house, it's not a pleasant feeling."