The nation's Roman Catholic bishops, continuing to develop their stance on the nation's economic life, yesterday released the second draft of a pastoral letter reiterating that concern for the poor must be the keystone of economic planning.

"The impact of national economic policies on the poor and the vulnerable is the primary criterion for judging their moral value," the bishops said. "Being a citizen of this land means sharing in the responsibility to shape and implement such policies."

Introducing the 40,000-word second draft, Milwaukee Archbishop Rembert G. Weakland said, "We do not back away from our strong conviction that more can and must be done to fight poverty and unemployment." Weakland is chairman of the drafting committee.

The pastoral calls the existence of 33 million Americans -- "about one in every seven people in our nation" -- below the official poverty line a "social and moral scandal" in a nation of vast wealth.

Although the nationwide unemployment picture has improved somewhat since release of the original draft 11 months ago, the second draft calls the recent 6 percent to 7 percent unemployment rate "morally unacceptable."

"The most urgent priority in U.S. domestic economic policy is the creation of new jobs with adequate pay and decent working conditions," it said.

Copies of the second draft have been mailed to the church's more than 300 bishops, who will critique it at their annual meeting here next month. Then, a third draft is to be prepared and submitted for final approval in November 1986.

A new emphasis in the second draft calls for scaling down the $300 billion annual defense expenditures. "Although some of these expenditures are necessary for the defense of the nation," the document said, "careful reductions should be made . . . to free up funds for social and economic reforms."

The question, the pastoral adds, "is not whether the United States can provide the necessary funds to meet our social needs but whether we have the political will to do so."

The new draft challenges the church to practice what it preaches by paying its employes equitable wages and permitting collective bargaining.

Catholic hospitals and school systems have been particularly resistant to collective bargaining with their employes.

A comment by Weakland that the bishops "took ownership" of the pastoral, plus enthusiasm expressed for it at the bishops' meeting in Collegeville, Minn., in June, indicate overwhelming acceptance of its general thrust.

Weakland said the Vatican has been "very supportive of our document" in two visits he made there to discuss it. "I feel no tension about it," he said.

Secular critics have charged that the document is a warmed-over version of some of President Lyndon B. Johnson's "Great Society" programs that were failures.

"Some Great Society programs did fail. Many did not," Weakland said. "With those that did fail, we have to ask why" and learn from the failures, he said.

"We call on the nation to resist the temptation to say that the present rate of unemployment and the present percentage of poverty in our society are the best we can do," he added.