Austrian Chancellor Bruno Kreisky won an unprecedented fourth term today as voters handed the durable 68-yard-old Socialist Party leader his most decisive victory in federal parliamentary elections.

The victory for Kreisky, who already has served longer as chief of government than any other current West European leader means another four years of Socialist Party rule for neutral but pro-Western Austria.

Initial official results, according to Interior Minsiter Erwin Lanc, give Kreisky's Socialists 96 seats in the 183-seat parliament. Almost 5 million Austrians voted.

For the past four years the Socialists have held a slim absolute majority of 93 seats, with the conservative People's Party holding 80 seats and the right-wing Freedom Party 10 seats.

According to the results announced by Lanc, the People's Party has dropped four seats, retaining 76, while the Liberal Party gained one, to 11. The Communist Party won less than 1 percent of the vote and no seats in parliament.

Some 270,000 absentee ballots remain to be counted and could alter the results slightly.

The results both delighted and surprised Socialist Party leaders, who were predicting a tighter finish.

Kreisky, who first become chancellor in April 1970, as head or a minority government, won reelection in 1971 and 1975 when the Socialists achieved slim but absolute majorities.

Throughout this campaign, Kreisky had declared repeatedly he would only serve again if his party won an absolute majority, since a conalition with conservatives would compromise his policies.

Yet, at a press conference just two days ago, the chancellor-reflecting the fears of a close race-hinted for the first time that if he fell one or two seats short he might be open to discussions that could gain him tacit support from some opposition parliamentarians.

The victory here tonight is widely viewed as a personal triumph for Kresiky rather than for his party. Kreisky, an internationally respected statesman whose reputation extends far beyond this country's political confines, is viewed as something of a father figure by many Austrians. He has also been successful at getting out a heavy vote in Vienna, a traditional Socialist stronghold.

It was estimated that about 90 percent of Austria's 5.2 million voters went to the polls.