Norway's Conservative Party, pledging to reduce taxes and introduce "supply side" economics into this oil-rich Scandinavian welfare state, will form a right-of-center government here next month after winning a postwar record share of parliamentary seats in a national election.

Despite a spirited campaign by Prime Minister Gro Harlem Brundtland, Scandinavia's first woman head of government, the left-leaning Labor Party was beaten by voter movement to parties promising lower taxes and less government bureaucracy. Labor, which has governed Norway for 30 of the 36 years since World War II, saw its representation in the 155-seat Norwegian parliament shrink from 76 to 69.

The Conservative Party, led by Kaare Willoch, a 52-year-old economist certain to become prime minister next month, increased its parliamentary seats from 41 to 52. It will try to form a coalition with the religious Christian People's Party, which won 15 seats, and the farmer-based Center Party, which won 11.

These parties also lost voters and parliamentary seats to the conservatives and may balk at joining them in a coalition, but they would still support a minority conservative government, as would two other small parties. A measure of the voter revolt was that 55 percent of the total vote went to right-of-center parties.

Willoch said tonight there was "a need for a coalition to get a dependable majority that would make it easier to implement our program in parliament."

The Conservatives do not intend to dismantle Norway's welfare state, but have promised to lighten the tax burden on individuals and businesses and to reduce government regulation. Willoch, a short, balding intellectual with sharp, bird-like facial features, said he believed tax cuts could spur economic growth while also reducing Norway's 14 percent inflation rate. Except for oil production from the North Sea, economic expansion has been relatively slow in recent years.

Willoch said he would "stick to my rule of gradual change."

Although he has promised, for example, to raise defense spending above the 3 percent annual increase already included in the Labor government budget that will dominate his first year in office, a senior Norwegian defense official said today, "I'm trying to calm down my colleagues who expect defense spending to double."

Willoch said tonight that he hoped "to bring greater clarity and less uncertainty to our foreign policy."

Willoch dissociated himself and his future government from a vocal campaign by the left-wing Labor Party to negotiate a nuclear-free Scandinavian zone with the Soviets.

"Any reduction in nuclear weapons can only come in negotiations between the nuclear powers," he said.

Although Norway has had two nonsocialist governments since the war, this is the first with a clear mandate to make significant policy changes.

Willoch said he thought it was possible for his Conservative Party to become the largest in a Scandinavian country for the first time since the war because voters realize it is not a threat to the welfare state. Conservative parties in neighboring Sweden and in Denmark also have gained ground significantly in recent elections.

The Christian People's Party, which champions traditional religious and family values in this Lutheran nation, holds the key to whether the Conservatives will govern alone or in a coalition. Negotiations will begin this week.

The religious party decided at a convention earlier this year to join a coalition only with a pledge to repeal the 1978 liberalization of abortion law in Norway, which allows a woman to decide for herself whether to have an abortion.

The center party intends to go along with whatever the Christian People's Party does. But the Conservatives decided to leave the abortion question up to their individual members of parliament, which elmiminates any possibility of the law's being repealed.

"There will be no change in the principle that the decision rests with the woman concerned," Willoch said. Opinion polls show that most Norwegians, even among Christian People's and Center Party voters, agree with this position and would favor a coalition.