Poland's Communist leaders, in a dramatic statement hinting at possible Soviet intervention, warned the nation today that it faced "economic and moral destruction" as a result of continuing labor unrest.

In a related development, the Polish Defense Ministry's military council held an emergency meeting today to express deep concern over the crisis, which, it said, posed a great threat to the security of the state, as well as to the social and economic order.

It added, "If the situation continues, it could produce a highly negative effect for the country's defense potential."

Taken together, the two statements amount to the gravest warning issued by the Polish authorities since the start of workers' protests more than five months ago. But there was no immediate sign of any heightened state of alert in Poland's armed forces or the country's political leadership and little evidence of tension among the population.

The wording and timing of the party statement, issued just after an important Central Committee plenum, appeared designed to bring home to the Polish people the serious dangers of fresh industrial strife. So far, most ordinary Poles have reacted with considerable skepticism to mounting speculation in the West about a possible Soviet invasion of their country.

The Central Committee statement was made in the form of an appeal to the Polish nation. It began: "Fellow countrymen, the fate of our nation and country hangs in the balance."

"Continuing unrest is leading our motherland to the brink of economic and moral destruction," it added. "We are still in a deep and severe political crisis. Its results could endanger our national interest."

The statement called on Poles to oppose the plans of "counterrevolutionary groups" who were propagating anarchy and chaos. It also appealed for a complete end to what it describes as "destructive strikes."

In fact, labor unrest in Poland has subsided significantly during the last few days, with leaders of the independent trade union federation Solidarity appealing for calm. Last week Solidarity's Warsaw branch called off a threatened general strike over the emotional issue of the power of the security apparatus following the release from detention of one of its activists.

Western analysts were puzzled by the timing of the Central Committee's appeal, which was released almost 24 hours after the end of the two-day plenum and at a time when no major strikes are underway. This appeared to suggest that it was prompted by events outside rather than within the country.

During the last few days, Western leaders, including President Carter, have warned of an unusual buildup of troops on Poland's borders. The latest statements from Warsaw indicate that these reports now are being taken seriously by the Polish leadership as well.

Recent speeches and behavior by Polish leaders do not, however, give any hint of panic. Following the Central Committee session, Communist Party chief Stanislaw Kania left Warsaw for a tour of mining regions in southern Poland and spoke confidently of the possibility of finding a peaceful way out of the crisis.

In Warsaw, there was no evidence of extra activity at Communist Party headquarters or government ministries.

It is not known how Poland's 320,000-strong armed forces would react in the event of a Warsaw Pact invasion. But there is a good chance that at least some units would offer resistance, and the Kremlin is presumably taking this possibility into account in arriving at any decision on whether or not to intervene here.

One of the reasons why the Army was not used to suppress the unrest along the Baltic Coast in August was because of doubts about its reliability in any action against workers. The defense minister is understood to have argued strongly in favor of a negotiated solution to the crisis from the start. a

The communique on the meeting of the military council appeared to be deliberately ambiguous. After warning of the danger to state security, it added: "The council has specified the tasks facing the armed forces under these circumstances."

Tantalizingly, the statement did not make clear whether the threat to Poland's security derived primarily from internal or external forces.

The Central Committee appeal called on the Polish people "not to waste our great common chance." It added that hopes for reform could only be realized in the framework of socialism, which provided the guarantee of Poland's continued independence.

In a concluding speech to the Central Committee plenum, which was released today, Kania said that the unstable position of the country had been aggravated by what he called the enemies of socialism.

"Let us say once again, unless we create a climate of social peace, everything else will lose importance," he said.

Kania added that he was aware of the concern felt by Poland's Communist neighbors about the crisis and said he had recently received letters from the leaders of the Soviet Union and East Germany promising aid.

The consensus of opinion among Western analysts in Warsaw is that the latest warnings amount to a final appeal to the Polish people to respect the limits of reform rather than a signal that an invasion is imminent.