The Reagan administration demanded yesterday for the first time that South Africa end the week-old state of emergency in violence-torn black townships, but announced that the United States would continue to resist economic sanctions against Pretoria.

"We want the state of emergency removed," presidential spokesman Larry Speakes said in a statement following an hour-long meeting of the National Security Council that President Reagan chaired before he left for a weekend at Camp David.

The statement marked an escalation in the administration's criticism of the emergency measures imposed July 20 in 36 South African cities and towns. The death toll has risen to 16 and the number of arrests officially stands at 910 since the white-minority government issued the emergency declaration, giving the police and army sweeping powers of arrest and seizure of property.

Earlier in the week, the White House did not ask publicly for an end to the emergency measures, calling on the South African government to excercise its "considerable responsibility" in a "scrupulous manner."

Speakes said the tougher language yesterday came because the "continuing violence and bloodshed has not abated and it is clear this is not bringing about the type of results that we want, or we would assume the South African government wants." In response to questions, he said the administration wants an "expedited" end to the emergency measures.

He said the administration has transmitted its demand to the Pretoria government through diplomatic channels.

Speakes said it does not indicate a "wholesale change" in the administration's policy of "constructive engagement" under which the United States has sought to influence South Africa away from its policies of apartheid, or racial segregation, by persuasion rather than public criticism or sanctions.

"We call on South Africa to act with the greatest restraint at this tense time," Speakes said in a prepared statement. "It is essential that the government in Pretoria respect the fundamental rights of all South Africans. The world is watching how that government and the South African police conduct themselves.

"The real cause of the violence in South Africa is apartheid," Speakes added. "A lasting peace will take hold in the townships and throughout the country only when apartheid is dismantled.

"We are deeply concerned whenever civil liberties are suspended anywhere in the world. This is certainly the case in South Africa, where violence and repression will not solve the country's problems."

Speakes reiterated the U.S. demand for "serious talks" between the South African government and black leaders "aimed at establishing a just society in South Africa and giving blacks political rights in that country."

He said the U.S. policy of constructive engagement must remain in place because "if there is no voice of reason talking with South Africa, it could lead to a result that no one wants." He said this result could be in policy terms or continuing violence, and said the administration had a "moral responsibility" to continue its approach to South Africa to preserve U.S. influence in events there.

Speakes said the South African government had made "dramatic moves in the right direction" in easing its apartheid policies, but "much more is needed, obviously." He lamented that the recent violence had "put a halt on a chance for progress."

Asked for details of the progress, the White House issued a list of changes in South African life in recent years, such as "substantial desegregation of hotels, restaurants, parks, libraries, theatres and sporting facilities."

While not commenting directly on a modified French resolution for voluntary sanctions adopted by the U.N. Security Council, Speakes said the U.S. opposes "mandatory" sanctions against South Africa. "We believe that to isolate South Africa economically and politically could lead to more bloodshed," he said. "Economic sanctions would do harm to the very people that we are trying to help."

Speakes stopped short of saying the United States would oppose voluntary sanctions against South Africa. France announced economic sanctions against South Africa earlier this week, and sanctions legislation has passed both House and Senate.

Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.) appointed conferees early yesterday to meet with House members to resolve differences between House and Senate versions of the sanctions legislation. This appeared to signal agreement that the two sides be seen as moving on the issue, even though no settlement of the differences is likely soon.

Lugar delayed naming Senate conferees for two weeks, trying to get House Democrats to accept the weaker sanctions in the Senate measure, warning that if they did not, Sen. Jesse Helms (R-N.C.) and other conservatives will filibuster the conference report.

The House Democrats in turn accused Lugar of foot-dragging to boost his measure, which they regard as too weak to have much effect. The conferees are expected to meet Wednesday.

Also yesterday, Rep. Mickey Leland (D-Tex.), chairman of the Congressional Black Caucus, asked Reagan for a meeting to discuss "the urgent need for an aggressive American response to the current atrocities" that have followed the emergency powers declaration in South Africa. Speakes said he had not seen the request.