It was welcome news to read of the Potomac River's "Remarkable Improvement" {Metro, May 14}.

Writer John Lancaster correctly credits President Lyndon Johnson with initiating the cleanup with the passage of the Water Quality Act of 1965. It was a proud moment for LBJ when he signed that act; he was one of the great environmental presidents of all times.

LBJ assigned me to write his remarks for the signing ceremony and instructed me to "get tough" with the polluters. He said, "I want the voters to know what their communities are doing to our rivers and lakes. I want stockholders to know what their companies are doing to our environment."

The president was especially interested in the Potomac -- where Teddy Roosevelt had once swum -- which he called "a river of decaying sewage and rotten algae."

In the "can-do" spirit of the Great Society, I committed the president to setting a goal. "With the signing of the Water Quality Act of 1965 this morning," I wrote, "I pledge to you that we are going to reopen the Potomac for swimming by 1975."

Before the signing ceremony, I cautioned the president that officials at the Department of Health, Education and Welfare thought it was a promise he could not keep; that the paragraph should be deleted. LBJ read over the speech draft and then said, "No, dammit, I'm not going to take that section out. The only way you can get the bureaucracy around this town to move is to hold its feet to the fire. You've got to set a goal and tell those people you expect them to meet it. Maybe we won't clean up the Potomac by 1975. Maybe it'll be 1985 or 1995. But we won't clean it up at all if we don't establish some priorities and expectations."

Today, LBJ would be enormously pleased to read in The Post that "some spots {in the Potomac} are clean enough for swimming." Twelve years late ain't too bad -- especially in the life of a river. ROBERT L. HARDESTY President Southwest Texas State University San Marcos, Texas