Reagan administration officials yesterday pleaded with a skeptical Senate Foreign Relations subcommittee for a near-doubling of military aid to Turkey, arguing that the Turks' decrepit army and air force endanger the southern flank of NATO.

Sen. Paul E. Tsongas (D-Mass.) said lack of a comparable proposal for Greece, Turkey's longtime antagonist, amounted to "blackmail" aimed at forcing Greek agreement to the continued presence of U.S. bases on its soil. Greece's newly elected socialist government has threatened to let the existing agreement with the United States lapse.

Richard R. Burt, assistant secretary of state for European affairs, testified that aid for Turkey would increase from $400 million to $755 million in fiscal 1984, while aid for Greece would remain stable at the 1983 level of $280 million. However, more aid for Greece will be requested "in the context of" a renewed agreement on the military bases, he said.

"Nobody is exerting any pressure," Burt added, saying the approach is "the most effective way to bolster an opportunity for getting an agreement."

Richard N. Perle, assistant defense secretary for international security, testified that the $1.79 billion proposal for aid to Turkey, Greece, Spain and Portugal is "sinew and bone" where cuts "would only . . . comfort . . . the Soviet Union."

Turkey's 500,000-man armed forces, second largest in NATO after the United States, has needs "greater than what we can get the Congress to accept" and will require increased aid later, Perle said. "Almost all major items are obsolete . . . . A strengthened Turkey would be an increased deterrent to possible Soviet expansion into the Middle East and Southwest Asia."

He attacked the 1974 U.S. embargo on aid to Turkey, imposed in the wake of Turkey's invasion of Cyprus, as "indefensible," saying that Turks have regarded U.S. aid as unreliable ever since.

Sen. Joseph R. Biden Jr. (D-Del.) disagreed, saying he is "much more worried about what happens to Greece in political terms" than about Turkey.