The general use of the pesticide DDT will no longer be legal in the United States after today, ending nearly three decades of application.

The general use of the pesticide DDT will no longer be legal in the United States after today, ending nearly three decades of application during which time the once-popular chemical was used to control insect pests on crop and forest lands, around homes and gardens, and for industrial and commercial purposes.

An end to the continued domestic usage of the pesticide was decreed on June 14, 1972, when William D. Ruckelshaus, Administrator of the Environmental Protection Agency, issued an order finally cancelling nearly all remaining Federal registrations of DDT products. Public health, quarantine, and a few minor crop uses were excepted, as well as export of the material.

The effective date of the EPA June cancellation action was delayed until the end of this year to permit an orderly transition to substitute pesticides, including the joint development with the U.S. Department of Agriculture of a special program to instruct farmers on safe use of substitutes.

The cancellation decision culminated three years of intensive governmental inquiries into the uses of DDT. As a result of this examination, Ruckelshaus said he was convinced that the continued massive use of DDT posed unacceptable risks to the environment and potential harm to human health.

Major legal challenges to the EPA cancellation of DDT are now pending before the U.S. Court of Appeals for the District of Columbia and the Federal District Court for the Northern District of Mississippi. The courts have not ruled as yet in either of these suits brought by pesticide manufacturers.

DDT was developed as the first of the modern insecticides early in World War II. It was initially used with great effect to combat malaria, typhus, and the other insect-borne human diseases among both military and civilian populations.

A persistent, broad-spectrum compound often termed the "miracle" pesticide, DDT came into wide agricultural and commercial usage in this country in the late 1940s. During the past 30 years, approximately 675,000 tons have been applied domestically. The peak year for use in the United States was 1959 when nearly 80 million pounds were applied. From that high point, usage declined steadily to about 13 million pounds in 1971, most of it applied to cotton.

The decline was attributed to a number of factors including increased insect resistance, development of more effective alternative pesticides, growing public and user concern over adverse environmental side effects--and governmental restriction on DDT use since 1969.