WASHINGTON (AP) _ An environmental group asked the Federal Trade Commission on Wednesday to investigate a series of television ads by Marine Shale Processors Inc., which claim the company turns toxic wastes into a safe, useful product.

The petition by Greenpeace USA Inc. alleges that the advertisements, which have run in Louisiana, where Marine Shale is located, and in the Washington D.C. area, are deceptive because, it maintains, the claim has not been scientifically proven.

The environmental group also challenged Marine Shale's claim that their process is ''environmentally safe'' because the company has been cited by Louisiana officials for allegedly violating state environmental laws.

Marine Shale, one of the countries largest toxic waste cleanup companies with $40 million in revenues last year, is contesting more than $4.5 million in proposed fines from the Louisiana Department of Environmental Quality.

The allegations brought by Greenpeace immediately were denied by officials of Marine Shale.

''We believe our product is exactly what we say it is,'' said George Eldredge, vice president and legal counsel for Marine Shale, in a telephone interview from Baton Rouge, La.

In one television ad, Marine Shale claims it turns dangerous toxic wastes into ''harmless reusable material'' and in another it says its process of incineration melts down the waste and ''make(s) it safe to use'' as aggregates for road construction and other uses.

The Greenpeace petition argued that these claims lack ''sufficient reasonable basis or scientific support'' and the company's claim it handles the wastes in an ''environmentally safe'' manner is suspect because of its problems with the Louisiana state officials.

The petition alleged that the advertisements ''mislead the consumers and the public to believe that the generation and disposal of hazardous wastes should not be a significant public concern because all such waste can be converted...into safe commercial product.''

Eldredge said Greenpeace's goal ''is to put us out of business.'' He said that the federal Environmental Protection Agency, state officials in Louisiana and many of the companies whose wastes are being handled have conducted tests on the aggregate produced from the wastes and have determined it to be safe.

Marine Shale, which has its plant in Amelia, La., about 75 miles southwest of New Orleans, uses a process in which wastes are heated to temperatures of more than 2,000 degrees. The company claims the process results in 100 percent of the waste being transformed into a nontoxic aggregate that is used as construction fill material and a base for roadways.

Last year Marine Shale handled toxic wastes from more than 2,500 companies in 48 states with revenues of $40 million.