After weeks of advance publicity, a government commission recommended sweeping constitutional changes today, including giving the vote to some minorities but not to South Africa's majority blacks. It also proposed creation of an executive president with almost unrestrained powers.

The proposal of the President's Council is the so-called "de Gaulle option," frequently hinted at in the past by supporters of Prime Minister Pieter W. Botha as the only way to enable him to persuade his reluctant white Afrikaner followers to accept changes in South Africa's racial policies.

The plan advocates the inclusion of Coloreds (persons of mixed race) and people of Asian descent in the Cabinet, and suggests that they be given representation in the presently all-white legislature on a basis to be worked out later.

The 21 million blacks, who constitute three-quarters of the country's population, are excluded.

A separate report dealing with local and regional government proposes that blacks be given a political say in the towns and cities of what is officially regarded as "white" South Africa. They can have national political rights only in 10 scattered tribal reserves, called homelands, which make up 13 percent of the land area of South Africa.

Immediate reaction to the proposals was mixed. The official opposition Progressive Federal Party, which favors the extension of political rights to all races, said it found merit in the local and regional proposals but was critical of the continued exclusion of blacks at the national level.

Relative moderates in the ruling National Party were delighted, interpreting the proposed rights for Coloreds and Asians as an important first breach in South Africa's strict political color bar.

There were widespread misgivings on the opposition side that the powers of the president were so unrestrained as to be dictatorial.

The plan's chief architect, Denis J. Worrall, a U.S.-educated political scientist, told a press conference that the proposals would move South Africa from a British system of parliamentary government to an U.S.-style congressional system.

However, observers here note, it has none of the checks and balances of the U.S. system. There is no judicial role limiting executive power, and the legislature is given no constraining authority.

There is no suggested mechanism for impeachment of the president, who would be elected for a seven-year term and be eligible for reelection.

The South African constitution contains no bill of rights or clauses protecting individual freedoms. It is a simple act of parliament, changeable at any time by a majority of one.

Because Worrall's panel is not ready yet with its proposals for extending political rights to Coloreds and Asians, it suggests that the first president be elected by the present all-white Parliament. Worrall said he hoped to be ready with the additional proposals by the end of next year.

The National Party took the decision three years ago to extend political rights to the 2.5 million Coloreds and 850,000 Asians, and at that stage adopted a complicated plan to have three separate chambers of Parliament for these two groups and the 4.5 million whites, but the plan was dismissed as impractical.

Black rejection of the government's homelands policy is almost universal. Many Colored and Asian leaders also reject it and refused to participate in the President's Council when it was established two years ago. There are signs, however, that the moderate Colored Labor Party may change its stance and accept an offer of Cabinet posts and seats in Parliament