Environmentalists are mounting new efforts to block U.S. funding of a fruit fly eradication project in Guatemala, even though the Agriculture Department has decided to stop using a cancer-causing pesticide that is banned in this country.

USDA's Animal and Plant Health Inspection Service (APHIS) decided to drop the carcinogen, EDB, after the Environmental Protection Agency ruled that it would not be acceptable after Sept. 30 for treating imported mangoes, the sole exception to the 1984 ban.

But the dispute over the Mediterranean fruit fly project, which APHIS is carrying out at a cost of more than $7 million a year, could erupt anew today when the Senate Appropriations Committee takes up the funding issue.

APHIS and the Guatemalan government have justified the project on the ground that fruit fly eradication would improve Guatemala's opportunities for exporting agricultural products, including coffee, to the United States. U.S. fruit and vegetable farmers have supported the project as a preventative step for protecting crops in this country.

The Natural Resources Defense Council and the Sierra Club, opponents of the Guatemala project, have continued to object on the ground that malathion, a potent broad-spectrum pesticide, will be sprayed over large areas containing villages, bodies of water and endangered animal species.

"The use of EDB was our most visible objection, but we continue to question the need and the urgency of APHIS' activities in Guatemala," said David Wirth of the council. "The benefits to the region are questionable -- and in fact, the coffee growers that APHIS says it is helping are protesting the project.

"I have yet to see anything to show that stopping this project would increase the Medfly infestation in the United States one iota," Wirth said. "It should be put on ice for at least a year until a full cost-benefit study is done" and the Agency for International Development (AID) completes its review.

"USDA should justify it on those grounds," he said.

The Association of United Coffee Growers, in a Guatemala City newspaper ad, complained that the "intense application" of chemicals and insecticides in the eradication project is "causing lower production of coffee, cardamom, cocoa and bee's honey." Malathion is toxic to bees, fish and shellfish.

The growers urged an end to aerial spraying conducted jointly by APHIS and the Guatemalan government, charging that it is "an immediate act of destruction for the health, the economy, the ecology and the production of our country."

Although the environmentalists protested, an Appropriations subcommittee, at the behest of Sen. Lawton Chiles (D-Fla.), last week approved an additional $1.5 million for Moscamed, as the fly-spraying project is called. But the panel cautioned that the new money could not be spent until the AID environmental assessment is completed.

AID administers PL-480 Food for Peace money that Guatemala intends to spend as its contribution to the project. The AID assessment is expected to be finished in April.

A House Appropriations panel chaired by Rep. David R. Obey (R-Wis.) has approved a bill directing AID to report to it before going ahead with Moscamed spending.