The board of the Metropolitan Washington Council of Governments said yesterday that the area's emergency warning system is "unreliable," plagued by sirens that either fail to sound when they are supposed to or that go off accidentally.

The board, composed of 24 local government officials, urged the Federal Emergency Management Agency, which maintains the system, to make improvements within six months or provide funds to COG to find alternatives to the current system. COG officials asserted that, according to FEMA's own estimates, 25 percent of the area's sirens were malfunctioning in March.

COG Board Chairman Gil Weidenfeld, who is the mayor of Greenbelt, said after yesterday's meeting that the nuclear plant disaster in the Soviet Union had "heightened everybody's sensitivity," and added: "You never know when a major disaster could occur."

John Sullivan, FEMA's chief of telecommunications in this region, said that COG's criticism was "very premature," because the agency had installed a new $1.2 million radio system to activate its sirens and the system was still in the "test and evaluation" stage. The old system still can be used as a fallback, Sullivan said, but he acknowledged that he could not say how much of either system is functioning properly.

"They the COG board jumped the gun by trying to paint a totally black picture . . . even though we haven't told anyone that the new system is up and ready to fly," Sullivan said.

The system consists of about 470 sirens in the District and suburban Maryland and Virginia that are part of the former Civil Defense system designed to warn the public of wartime attacks, according to Edward V.J. Putens, chairman of COG's Public Safety Policy Committee. The sirens also have been used for years to warn the public of such peacetime disasters as tornadoes, hazardous chemical spills or serious accidents.

But few people know the meanings of the different siren blasts and, even when the sirens work properly, "the sounding of sirens is largely ignored," Putens told the COG board yesterday.

In its resolution, the board also urged FEMA to begin "a concerted effort" to educate the public to the meaning of the sirens.

According to Thomas P. Rametta, the principal public safety planner for COG, there have been numerous incidents of sirens malfunctioning. In Mount Rainier, a siren at a closed junior high school blared for 2 1/2 hours recently for no reason, before local officials came to turn it off, he said.

About a year ago, all the sirens went off at 6 a.m. and local governments "were inundated with calls about what was going on," according to Rametta. FEMA officials at the center in Olney, where the sirens are managed, were unaware of the problem because it had not registered on their computers, he said.

Rametta said that COG's Disaster and Emergency Preparedness Committee had been working with FEMA "for some time" on the problem, and two years ago, when the agency began installing the new system, the group believed that the problem would be alleviated. Instead, Putens said: "Unfortunately, now the system is even more unreliable than ever before."

Sullivan disagreed. He said that while he does not dispute COG's charge that 25 percent of the sirens were malfunctioning in March, the figure is "not very meaningful" because problems are fixed each day and the backup system on those malfunctioning sirens might, in fact, be working.

"Absolutely, I'm concerned about it," Sullivan said. "That is why we are spending $1.2 million to upgrade it."