JOHANNESBURG, NOV. 7 -- Black nationalist Govan Mbeki, speaking at a tumultuous news conference cordoned off by riot police, defiantly dismissed the South African government's recent reform measures today as an "escapist policy playing around the basic issue" of political rights for blacks.

Mbeki, who was released from prison Thursday after serving 23 years of a life sentence for sabotage and plotting to overthrow the government, called on blacks to boycott a proposed national council designed to negotiate power-sharing among the races.

Police carrying assault rifles and dressed in riot gear cordoned off the downtown office building where Mbeki spoke and ordered scores of reporters and photographers to leave the "unrest area" immediately after the news conference, spraying some with cans of tear gas to keep them moving.

There appeared to be no sign of unrest as a small crowd waited outside the building for Mbeki and his party to leave.

As a declared member of the outlawed South African Communist Party, Mbeki is a "listed" person and may not be quoted in South Africa. At a news conference Thursday in Port Elizabeth, Mbeki spoke under a special government waiver of the ban, which officials said was valid for that appearance only.

In his news conference today, Mbeki rejected the notion that any conditions had been placed on his release and spoke openly before a half-dozen television cameras.

Mbeki called the government's proposed national council an attempt to create an advisory panel patterned after a string of failed advisory bodies dating as far back as 1894.

"We would really appeal to them {black leaders} to keep out of it because it is not taking them anywhere . . . . Anybody who goes there deliberately and willingly knows there's no milk in it," Mbeki said, gesturing as if milking a cow.

Mbeki, a former chairman of the outlawed African National Congress, was in almost constant telephone contact with ANC headquarters in Lusaka, Zambia, yesterday. Last night he said that all decisions on his political activities and major statements would be coordinated with the exiled ANC executive committee.

Mbeki said he had discussed the issue with imprisoned ANC leader Nelson Mandela during an hour-long meeting Thursday at Cape Town's Pollsmoor Prison. Mandela, Mbeki said, was also against black participation in the proposed national council.

Also attending today's news conference was Mandela's wife, Winnie, who said to Mbeki, "We are almost ashamed to introduce you back to the same conditions you fought against" before being imprisoned.

Describing Mbeki as a "barometer through which the Afrikaner is measuring the political mood of the country," Mandela advised blacks to be cautious with their optimism about the release of other imprisoned ANC leaders.