A serious internal split on the merits and dangers of President Reagan's effort to turn programs and powers back to the states caused the National Conference of State Legislators (NCSL) today to take a strictly neutral, wait-and-see posture on the Reagan federalism initiative.

With each state casting one vote, the delegates split 23 to 22 in favor of a neutral amendment that deleted most praise of Reagan's initiative and said, "We do not endorse or reject the proposals which have been presented to date" in the ongoing negotiations between White House officials and state and local government representatives.

The amendment deleted language that had been endorsed by the organization's conservative-dominated executive committee, which "welcomed the steps taken by President Reagan" and praised his "bold step" toward sorting out federal and state responsibilities.

Critics complained that the language implied approval of proposals which might cost the states billions and reduce services to the elderly, children and the poor.

The main resolution expressed the legislators' determination that the federal government should retain primary responsibility for income guarantee programs, food stamps and Medicaid while the states assume education, transportation, law enforcement and other programs.

The intense debate and close vote, a rarity in the history of this organization, represented a shift of power from conservative and Sunbelt legislators to an emerging group of urban and liberal legislators.

That same shift is reflected in the succession to the organization's presidency, with New York Assemblyman William Passannante, a liberal Democrat, taking over from Kansas Senate President Ross O. Doyen, a conservative Republican.

The old-guard executive committee had tabled a similar amendment yesterday, but backed off today when opposition from black and liberal legislators from New York, Illinois and other urban states threatened to block passage of the original resolution by the required three-quarters vote.

After the Illinois-sponsored amendment was adopted by one vote, the amended resolution passed by a wide margin.

This was the second setback suffered by the White House during the regular summer schedule of meetings of associations of state and local elected officials. Earlier, a supportive resolution had to be withdrawn at the convention of the National Association of County Officials.

The main stumbling block has been Reagan's insistence that the largest cash welfare program, Aid to Families with Dependent Children (AFDC), should be turned over to the states.

The governors and legislators both have resisted that, and the NCSL today reaffirmed its position that the federal government should assume "primary responsibility" for income security programs, along with Medicaid and food stamps. Reagan has agreed to the latter two programs being financed from Washington, but has balked on AFDC.

The legislators said they would take over "primary responsibility" for education, transportation, law enforcement and other programs, but reiterated that, "The goals of new federalism must not result in an increase in state expenditures as the price of curbing spending and budget growth at the federal level."

On two other controversial issues, the NCSL failed to win the three-fourths' majority its rules require for adoption of a policy position. By a vote of 27 to 19 the states favored a three-month delay in the cost-of-living adjustments on all federal entitlement programs, and unspecified limits on future cost-of-living adjustments.

And by a vote of 28 to 19 they favored a call for a nuclear freeze, with the funds saved from weapons development to be used for domestic programs.