WARSAW, Poland (AP) _ Voters in Poland's first referendum in 41 years rejected political and economic reforms that would have meant painful price increases next year, diplomatic sources said today.

The double defeat - if confirmed by officials - would represent a stunning blow to the government of Polish leader Gen. Wojciech Jaruzelski, which strongly campaigned for the two measures in Sunday's plebiscite. .............................BULLETIN........................................

Voters rejected political and economic reforms that would have meant painful price increases next year, diplomatic sources said today.

The double defeat - if confirmed by officials - would represent a stunning blow to the government of Polish leader Gen. Wojciech Jaruzelski, which strongly campaigned for the two measures in Sunday's referendum, Poland's first in 41 years.(1236EST) .............................................................................

The sources said Western diplomats learned the results at a meeting with Foreign Minister Marian Orzechowski.

According to the sources, for the first question, on a program of radical economic reform that would have meant average 40 percent price increases next year, 44 percent of eligible voters saying ''yes.'' For the second question, on political reform, 46 percent said ''yes,'' the sources said.

The government had said previously that if it lost the referendum, reforms would continue, but at a slower rate.

Polish law requires referendum questions to be approved by a majority of all eligible voters. It appeared that more of the votes actually cast on Sunday were for the questions than against them.

A relatively large number of no-shows at the polls made the difference.

Opposition activists had dismissed the referendum as a charade and demonstrations against it were staged Sunday in several cities, including marches that were dispersed by police in Gdansk and Warsaw.

At least 12 people in three cities were detained.

The Communist government said about 68 percent of Poland's nearly 26.8 million eligible voters participated.

Jaruzelski had strongly endorsed the referendum as a step in the ''socialist renewal'' of Poland in the years since the 1981 crackdown on the now-outlawed Solidarity independent labor federation.

Poles were asked to approve radical reforms to make Poland's sluggish, debt-plagued economy more market-oriented, and promising prosperity after two or three years of austerity.

They were also asked if they favor a ''Polish model of democratization,'' that would likely include giving more power to local governments and opening up high-level positions to people who do not belong to the Communist Party.

There was no immediate announcement of the results by the government. Government spokesman Jerzy Urban scheduled an evening news conference that did not start on time.

Solidarity leaders, though advising people not to vote, did not wage and active boycott campaign.

At a news conference early today, Urban denied a Solidarity statement advising voters to consider the referendum propaganda significantly held down voter turnout.

Fear of price increases and weariness with the difficulties of everyday life in Poland's moribund economy had a greater effect in discouraging voters, he said.

The largest of the anti-referendum protests took place Sunday in Gdansk, the birthplace of Solidarity. Opposition activists said at least 2,000 people began a march after a Mass but were stopped by police armed with truncheons.

Urban confirmed the demonstration but said only about 400 people were involved. He denied that police beat demonstrators and charged that some protesters stoned the officers. Two people were detained, he said.

After a pro-Solidarity Mass in Warsaw on Sunday night attended by more than 5,000 people, reporters saw about 1,500 people carrying union banners try to march to a nearby square before being blocked by police.

In Nowa Huta, a Krakow suburb, about 500 people marched to a polling station and in Wroclaw, about 200 anti-government protesters rallied, opposition activists said. No incidents were reported.

In Wroclaw, four people were detained in a separate demonstration at a polling station, the official media reported.

Urban said police detained six opposition activists who unfurled a banner from a roof near the U.S. Consulate in Krakow reading: ''Our vote in referendum: the PZPR (Communist Party) to Madagascar.''

In contrast to the protests, many voters interviewed at polling stations appeared to relish the chance to voice their views and said they hoped that the election would improve life.

''I am a Pole and this country's fate is as valuable to me as my own life,'' said a middle-age telex operator.

The turnout was lower than the June 1984 general election to people's councils in Poland, which the government said drew about 75 percent of the electorate, despite a Solidarity boycott.

Before the rise of Solidarity, elections in postwar Poland typically attracted 99 percent of the electorate, according to official figures.

Poland's last nationwide referendum was held June 30, 1946, when communists were consolidating power in the country following the war.