South Africa's Parliament today opened what has been labeled here as its "most important session in history." On the first day, however, there were no signs that the government will launch any major policy changes to answer the problems of growing racial tension, economic woes and political polarization.

The 171-member, all-white body has not met since the first race riots broke out on June 16, 1976, nor since the price of gold dropped dramatically, dealing a devasting blow to the South Africa economy and the black employment situation.

The opening of Parliament coincided with a new controversy that again threatened race relations. Two government education officials warned that they may close down four Roman Catholic private schools that have admitted non-white students this term.

An atmosphere of tense expectation has spread through the country as both blacks and whites wait to see what legislation the government of Prime Minister John Voster introduces in response to the recent turmoil.

In the opening address in Cape Town this morning, President Nicolaas Diederichs pledged the government would make "adjustments" in its racial policies this session.

"The government is firmly resolved to create for all our people irrespective of race or color, a dispensation that will secure peace and ensure human dignity and opportunity for all," Diederichs said.

"Justifiable changes of this nature have been made in the past as a matter of course and are at present being made by the government with a view to a better and brighter future," he said.

Kiederichs indicated, however, that the moves would not alter the overall policy of apartheid, or separation of the races. The only move anticipated in the coming five-month session is a restructing of the powerless urban Bantu (black) Councils to introduce new executive powers. White administration boards, however, are still expected to have ultimate authority.

One of the 40 bills to be introduced this session is a new criminal procedures bill with 350 clauses, intended to strengthen police and judicial powers.

The new budget is expected to include request for an increase in the defense budget of approximately $460 million, bringing the defense budget to more than $2 billin.

The cornerstone of apartheid - the carving of nine independent countries for South Africa's 18 million blacks out of small African tribal reserves - will not be altered. Among the actions scheduled for the new session is legislation that will allow the Bophuthatswana tribal reserve, about 150 miles west of Johannesburg, to gain independence later this year.

The status of South Africa's 2.3 million "coloreds" (people of mixed race) is also not expected to change this year. The government has indicated it will issue a policy paper on the recommendations of the Theron Commission - a three-year study that calls for parliamentary representation for "coloreds" and removal of discrimination laws affecting them - but that it will not introduce any of the legislation recommended.

The tough tone of this year's Parliament was revealed when Diederichs blasted the United Nations for "impeding" peace in South Africa with its "virulent and unbridled attacks" that he says "cynically disregard" the facts. "The government has no intention of yielding to pressures of this kind," the president warned.

He said that the government intends to take an increasingly strong stand against the "subversives" responsible for six months of on-and-off racial violence that have claimed the lives of more than 500 blacks and against the "steadily encroaching Marxist political and military danger in southern Africa."

Diederichs also indicated that millitary callups would increase to meet new demands on the regular army and citizen forces, and that civil defense measures would be improved.

The ruling National Party is expected to have little trouble pushing through these measures since the official opposition, the United Party, has been weakened by a major split this week, losing mix members of Parliament.

It is expected that the United Party and the Liberal Progressive-Reform Party will eventually merge to form a stronger opposition, but after six months of discussion the move is still on the drawing boards.

In an attempt to reassure the public after six months of internal turmoil, Diederichs said South Africans should not be "unduly pessimistic" about the future, that the government aimed to build up the country so it would "continue to be an asset to the world."

Government officials moved quickly to condemn the Catholic schools who have admitted non-white students.

"If non-whites are allowed into white private schools their registrations will be withdrawn. It must happen," Sybrand Van Niekerk, administratir of Transvaal Province, said today.

Cape Province administator L. A. Munnik warned two Catholic girls schools, which admitted "colored" students, that they must ask the girls to leave immediately or be closed forthwith.

Father Dominic Scholten, spokesman for the education department of the South African Catholic Bishops Conference, pledged today that the church would continue with integration regardless of the government's actions.

"We are no longer free to tolerate a situation that fosters discrimination," he said, adding, "The present situation in South Africa will not permit a move against the church."