The Pentagon yesterday took its hardest public line to date on the military buildup in the Caribbean, declaring "contingency plans" are being drafted "to respond as required to further military threats and acts of aggression."

In the same statement, Fred C. Ikle, undersecretary of defense for policy, told a Senate Foreign Relations subcommittee that the Pentagon will train about 1,600 Salvadoran soldiers to help El Salvador meet the heightened threat.

Although drafting contingency plans is standard procedure for the Pentagon, they are seldom announced in the pointed way Ikle chose yesterday. The Joint Chiefs of Staff, in response to the hardening rhetoric of their civilian bosses, recently ordered its planning staffs to take a fresh look at the military options for the Caribbean.

However, military leaders who have focused on ways to combat the aggression Ikle decried yesterday see no quick fix. Helping friendly governments in the Caribbean upgrade their armies, navies and air forces seems to be the Pentagon's plan for now.

Ikle said the United States will train up to 600 Salvadoran army officer candidates, an undisclosed number of sergeants and other noncommissioned officers and a light infantry battalion of 1,000 men.

"The need for better trained military leaders is compelling," Ikle said. "We must halt terrorist aggression and deter further military attacks in the hemisphere."

The Pentagon executive's tough rhetoric was in line with testimony given to the same subcommittee Monday by Thomas Enders, assistant secretary of state for inter-American affairs.

Ikle gave the subcommittee this rundown on the military threat in the Caribbean:

Cuba has received from the Soviet Union 63,000 metric tons of arms so far this year, highest since the Cuban missile crisis year of 1962.

Cuba has an army of 225,000 men; a navy of 11,000; air force of 16,000, and "hundreds of thousands of para-military forces that in many instances are better trained and equipped than the regular armed forces of other Caribbean countries.

"The Cubans have over 200 Mig fighters, 650 tanks, 90 helicopters, two Foxtrot attack submarines, one Koni class frigate and about 50 torpedo and missile boats--clear and convincing evidence that Cuba is truly a highly militarized society with a growing military capability."

The Cuban military presence in Nicaragua consists of up to 5,000 civilian advisers and 1,500 military ones, a force tipping the country into the Soviet-Cuban grasp.

These Cubans are being assisted by East Germans, Bulgarians, North Koreans and Soviets in building the Sandinista army from 60,000 to 250,000, which would mean "one in 10 Nicaraguans under arms." Bulgaria is training 70 Nicaraguans as jet pilots in Bulgaria.

Ikle complained that "our European allies are much too insouciant and cavalier about the growing military threat in the Caribbean," especially since much of the cargo destined for Europe must sail through the Florida Straits in easy striking distance of Cuba torpedo boats and planes.