JOHANNESBURG, JUNE 21 -- The South African government charged today that the African National Congress was "dragging its feet" on negotiations that eventually could lead to a new constitution and criticized the ANC's leader, Nelson Mandela, for continuing his support for armed struggle.

Gerrit Viljoen, minister in charge of constitutional affairs and the government's chief strategist on negotiations, said the ANC had put off until July 10 any decision on a draft accord on the release of political prisoners, while the government had already agreed to it.

The draft accord, which deals with the return of exiles, the definition of political prisoners and plans for their release, was submitted for approval to the government and the ANC National Executive Committee May 21.

"The ANC is once more dragging its feet," Viljoen said.

Viljoen's criticism coincides with Mandela's visit to the United States and may have been partly motivated by a government desire to try to persuade the American public that Pretoria is not to blame for delaying negotiations between white and black leaders on a new constitution for South Africa.

Viljoen said the government expects those negotiations to start early next year and that he expects substantive results within two years.

The ANC has never made clear why it wanted so much time to make a decision on the proposed accord regarding the return of exiles and release of political prisoners. Such an accord could resolve two of their main demands upon the government for creating an atmosphere conducive to negotiations.

Critics have charged that the ANC is deliberately delaying any decision because a release of political prisoners would go a long way toward meeting one of the main conditions many Western governments have set for an easing of economic sanctions against South Africa. The 12-member European Community is holding a summit June 25 in Dublin, where the possible lifting of sanctions will be debated.

The freeing of all political prisoners is one of five conditions specified in the Comprehensive Anti-Apartheid Act passed by the U.S. Congress in 1986 for presidential consideration of a lifting of some U.S. sanctions.

The Star, Johannesburg's main English-language daily, reported tonight that government delegations involved in working out the proposed accord on political prisoners had agreed to release all political offenders, including those involved in murder and bombings, in phases according to the seriousness of their crime.

But government agreement to this approach depends upon the ANC's abandoning of armed struggle, the newspaper said.

ANC sources have indicated that their organization is ready to "suspend" the armed struggle if the government does in fact meet demands for a release of political prisoners and if it also provides amnesty for the country's estimated 20,000 political exiles.

Mandela told a press conference in The Hague last week that the ANC was negotiating for the release of "almost 1,000 political prisoners," while the government accepted that 577 people fall into that category.

Earlier, some ANC officials cited a figure of 3,000 or more political prisoners, but that figure apparently included detainees and some people convicted under the common criminal code. Human-rights groups have estimated the number of political prisoners to be as high as 3,500, including those held in the nominally independent black homelands.