South Africa's white electorate was returning Prime Minister John Vorster's ruling National Party to power today with a larger majority than it received in the last election in 1974, according to early results.

The National Party clearly won increased support from the English-speaking sector of the population. The United Party, traditionally the party of English speakers, disbanded last June and the opposition since then has been divided between two parties.

It appears that Vorster, who called for the elections unexpectedly last September, is receiving the mandate he requested to show white South Africa's determination to reject outside pressures to alter its policies of separate development (apartheid).

With the results in from nearly half of the 165 parliamentary constituencies, National Party candidates hold about 75 seats. In addition to the 42 uncontested seats it is retaining, it has taken four seats from the opposition.

In some districts, the National Party gain has been spectacular. In Vorster's home constituency of Nigel, for example, the prime minister won with a majority of more than 9,000 votes. In 1974 his majority was a little more than 6,000 votes.

This election was not expected to alter the National Party's 29 years of uninterrupted rule in South Africa, but the size of its majority is being taken as a gauge of the white population's approval of the party's present policies.

Early trends show that the voters are giving the National Party one of its biggest, if not the greatest, majority since it first came to power in 1948. In all the seats decided so far, it has won 71 per cent of the vote, increasing its majority.

Some of the former United party constituencies, however, have rejected the National Party and have gone to the Progressive Federal Party, which is being tapped to become the official parliamentary opposition in this election.

The Progressives, who went onto the contest holding 18 seats, have gained three seats formerly held by the United Party and have received 16 per cent fo the votes so far.

A rival to the Progressive Party for the opposition role, the New Republic Party was not faring so well. Early returns gave the Party two seats to the Progressives' five.

The ultra-rightwing Herstigte Nasionale, which advocates absolute white minority-rule without any concession to the black majority, were taking a severe beating at the hands of the National Party.

The election proceeded quietly throughout the day despite fears that militant blacks might attempt to disrupt the balloting. South Africa has been troubled by violence over the past 17 months triggered by black demands for a share in political power.