Sen. Wojciech Jaruzelski announced today that plans to lift martial-law restrictions had been delayed because of continuing social and industrial unrest.

In a keynote speech to the Central Committee of the ruling Communist Party, the Polish leader harshly attacked the West, particularly the United States, for imposing economic sanctions following the military crackdown on Dec. 13. He said that, as a result, Poland would have to rely more heavily on the Soviet Bloc.

The Central Committee meeting, which continues Thursday, is the first for the party's ruling body since the imposition of martial law. It was billed in advance as a crucial stage in a campaign by the party to regain public confidence and reassert its damaged authority.

Jaruzelski's marathon 68-page speech underscored the painful dilemma faced by the Polish leadership in its attempts to return the country to civilian rule.

Jaruzelski attempted to steer a centrist course between the demands of hard-liners who have been calling for tougher action against "the opponents of socialism" and reformers who say the party can only restore its credibility by rebuilding bridges with society. He laid much of the blame for present economic and political problems on the Reagan administration, which he accused of fueling "counterrevolution" in Eastern Europe.

Dressed in full military uniform, Jaruzelski told the 200 Central Committee members that martial law did not mean the end of reforms endorsed at an extraordinary party congress in July 1981.

"Martial law is not an end in itself. We regard it as a phase in recovering our balance," he said.

The 58-year-old Army general--who holds the posts of party chief, premier, and defense minister--said that what he termed "inconveniences" caused by martial law gradually were being eased. Further relaxations would be announced in the next few days.

But, in what was seen as a public acknowledgement of the opposition to the martial-law authorities, he added: "It is not possible to lift the restrictions to the extent we intended. This is prevented by continuing tension, extremist acts, and poster campaigns."

In a speech to the national assembly, the Sejm, on Jan. 25, Jaruzelski promised that many of the most burdensome martial-law regulations would be lifted by the end of February, provided the country remained quiet. It was assumed at the time that the measures he had in mind included a relaxation of the night curfew, severe restrictions on travel, and tight controls on telephone and telecommunications links within Poland and with the outside.

The past few weeks have seen the easing of a communications blackout and the reopening of some newspapers. But the awesome machinery of military control remains very much in evidence--and, to a foreign journalist returning to Warsaw after three weeks' absence--the Army's presence in the streets seems undiminished.

Officials have acknowledged demonstrations and other protests against martial law in Gdansk, Poznan, and Warsaw. Underground activists of the suspended independent Solidarity trade union have concentrated on spreading information through pamphlets and wall slogans. There have also been the first scattered signs of urban guerrilla warfare, including the shooting of a policeman and several bombings.

Jaruzelski drew attention to the government's fear of terrorism by recalling that, during the late 1940s when the Communist Party was first consolidating power, 30,000 Poles had died in what amounted to a limited civil war.

He warned: "Even today there are those who are attempting to organize opposition activities, dabble in conspiracy, or carry out acts of terror and sabotage. They must know that they cannot count on leniency. Such adventurism delays a return to normality and poses a threat to the reviving economy."

The party chief accused Western intelligence services of preparing for counterrevolution in Poland--and of being bitterly disappointed when their plans were foiled as a result of martial law. Now, he said, the activity of "subversive foreign radio stations" was being intensified and a new slogan was being trumpeted: "The winter is yours, but the spring will be ours."

Turning to damage to the Polish economy, which Jaruzelski blamed on U.S. sanctions, he said suspension of deliveries of American corn feed would result in a drop in chicken production from 505,000 tons to 70,000 tons. He predicted that this would mean the average Pole would consume seven kilos (16 pounds) less meat and 25 fewer eggs per year.

The Polish fishing fleet stood to lose $20 million because of a ban on fishing in American territorial waters, he said, and other industries would also have to cut back because of raw-goods shortages.

Jaruzelski said he had received a message from Soviet President Leonid Brezhnev promising increased deliveries of such materials as cotton, wool, artificial fibers and synthetic rubber. He did not cite amounts but said the supplies would allow many factories to remain in production.