Nearly half of 1,246 hazardous-waste dumps surveyed in a congressional study show indications of ground water contamination and that Environmental Protection Agency monitoring of the sites is "inaccurate, incomplete and unreliable," a House Energy and Commerce subcommittee reported yesterday.

The survey found that despite "some indication of ground water contamination" under 559 disposal facilities, federal enforcement of antipollution requirements "has been dilatory and seriously deficient."

The subcommittee also found that "an extremely high" number of waste facilities have not installed the ground water monitoring wells legally required by November 1981.

"Some of the data are shocking, especially when viewed from the perspective that the regulations called for compliance . . . 3 1/2 years ago," committee Chairman John D. Dingell (D-Mich.) wrote in a letter to panel members.

"According to the EPA," Dingell said, "ground water contamination is the most serious potential threat to human health and to the environment created by the disposal of hazardous wastes."

The study was intended to determine the degree of compliance with the Resource Conservation and Recovery Act, which requires hazardous-waste dump operators to install monitoring wells to ensure the purity of the water table beneath the sites.

It found that 25 percent of the sites had inadequate wells, another 15 percent had no wells and in 17 percent of the cases the EPA was uncertain of how adequate the wells were.

Of the 317 sites with inadequate wells, the EPA either had taken no action or sent only informal warnings about more than half, the study found.

The study echoes findings by an EPA investigation last summer that found that a number of state governments have been lax in enforcing ground water monitoring laws. An EPA spokesman said the high proportion of sites with ground water contamination cited by the subcommittee might be misleading because the statistical sampling techniques used can yield a high rate of false indications of contamination.

While acknowledging the widespread noncompliance, EPA officials said the agency is continuing to review the problem and will take immediate action if contamination at any site appears to threaten human health or the environment.

In his letter, Dingell said he hoped that publication of the study will spur the EPA and the states "to make an all-out effort toward obtaining immediate compliance." The subcommittee is scheduled to hold hearings on the issue today.