WARSAW, DEC. 15 -- Poland's communist leadership signaled its intention to move ahead with a moderated version of its reform program today, announcing steep food price increases for next year, approving a platform for political liberalization and promoting a leading party liberal to the ruling Politburo.

Two weeks after failing to win a majority vote in a national referendum on the reform, authorities announced plans for a 40 percent increase in basic food prices next year, well below the 110 percent planned before the plebiscite but still more than double the increases pushed through this year.

At the same time, a key meeting of the Central Committee of the governing Polish United Workers Party elevated Mieczyslaw Rakowski to the Politburo, restoring to prominence an activist who symbolized the party's liberal wing in the 1970s and served as a chief government negotiator with the free trade union Solidarity in 1980-81.

Speaking at the close of the Central Committee session tonight, communist leader Gen. Wojciech Jaruzelski said the party had "confirmed the further democratization" of Poland, adding that the Politburo had been authorized to draw up a timetable for implementing specific political reforms.

Among the steps, outlined in a broad political platform approved by the Central Committee today, are changes in electoral law to allow more opposition candidates, devolution of some central government powers to local authorities, the legalization of moderate opposition groups in the form of debating clubs and the creation of a second chamber of parliament.

However, the party meeting appeared to stop short of the strong commitment to change in Poland's economy and political system hoped for by liberal activists. An expected shakeup of senior party officials failed to take place, and even Rakowski's advance fell short of the promotion to chief of ideology that his supporters had hoped for.

Polish analysts said the day's events appeared to represent an overall gain for reformers within the Polish party, but indicated that Jaruzelski continues to face conservative party resistance even as his ministers struggle to modify price measures strongly opposed by the Polish public.

In one speech to the plenum, Prime Minister Zbigniew Messner said the leadership now faced the question of whether it could pursue the reforms consistently or would "agree to a weakening of them that could push us into inactivity and stagnation."

In opening the meeting, Jaruzelski, speaking for the first time since the referendum setback, said "the conclusions stemming from it are many-sided and complex." The general argued that the result "does not give any basis for a view that our society is against the reforms," but added, "we do not want to sidestep the fact that a considerable and legally significant part of society has doubts and apprehensions" about the program.

Jaruzelski added that the Polish authorities would continue and even broaden the practice of referendums, holding them on the local as well as national level to decide key issues.

Messner, who outlined the government's economic plans for next year, said that while food prices would go up about 40 percent, overall price increases would average 27 percent, about one-third below the level planned before the plebiscite. He indicated that authorities would seek to keep increases in incomes at the level of overall inflation and thus well below food prices.

Though drastically modified from its radical prereferendum shape, the price and income plan is the toughest that Jaruzelski's government has attempted to implement since it ruled the country under martial law in 1982. In more recent years, authorities have attempted modest real increases in consumer prices but in practice have been unable to prevent wages from rising faster than food prices.

In moving to promote Rakowski, Jaruzelski appeared to be sending a signal to the party that the leadership remains committed to reform, party activists said.

A former editor of the influential weekly Polityka, Rakowski is well-known both at home and abroad as a leader of communist liberals. He maintained strong contacts with opposition intellectuals in the 1970s before becoming the government's negotiator with Solidarity during its legal existence.

Rakowski's performance ultimately earned him the emnity of both the opposition and the Soviet leadership of Leonid Brezhnev, which once vehemently denounced him by name in the Moscow press. In 1985, he lost his post as a deputy prime minister and became vice-marshal of the Polish parliament, a relatively minor post.

Three new department chiefs in the Central Committee bureaucracy also were named today. Party sources said the appointments marked the beginning of a shakeup in the central party apparatus that could lead to the abolition of about 250 of its 650 jobs.