The Philippines has very quietly annexed a large part of the disputed Spratly Islands, thus risking renewed tension in the area and at least a diplomatic blast from the other claimants -- Vietnam, Taiwan and China -- on a potentially explosive issue.

A government official gazette published on Feb. 19 laying down the claim on the potentially oil-rich islands the Philippines called the Kalayaan island group went unnoticed.

The Philippines thus had gone ahead with the legal claim in spite of earlier agreements with Vietnam's Premier Pham Van Dong and Chinese Vice Premier Li Xiannian during their visits here last year to settle the dispute through peaceful negotiations.

Although the pledge to peaceful talks may not preclude the Philippines' legal move, it may have strong political repercussions.

[The U.S. State Department views Manila's latest move as just as reiteration of an old claim rather than a full-fledged annexation, a department spokesman said Thursday.]

[U.S. officials denied a Philippine claim that America is bound to come to Manila's aid over the Spratly Island issue under the mutual defense pact signed between the two nations. The United States has tried to avoid entanglement in Asian territorial disputes.]

[Just why the Philippines has chosen to stress their claim again is somewhat of a puzzle, U.S. officials said. One expert specualted that the recent action may be a legal tactic in connection with current multilateral talks on the law of the sea.]

A decree signed by President Ferdinand Marcos and dated June 11, 1978, stipulates that the area within the boundary of the Kalayaan group "shall belong and be subject to the sovereignty of the Philippines."

The Philippines had fortified seven islands but the decree neither names those islands nor stipulates the number. The decree merely refers to the Kalayaan (freedom) island group.

The decree annexing the Spratlys was made public only after the signing of the revised bases treaty with the United States in January. The Philippines seems to have taken opportunity also of Vietnam's preoccupation with Cambodia at that time.

According to Decree No. 1596, control of the area is under the minister for national defense. The decree states that the claimed area is to be within certain longitudes and latitudes, which when a line is drawn accordingly seems to cordon off a hexagon-shaped boundary, enclosing many of the 57 islands in the Spratlys.

Within this hexagon are the Reed Bank, the Taiwanese-occupied island of Ito Aba, and some of the Vietnamese-held islands. It barely skirts the main Spratly island, occupied by Vietnamese troops.

Vietnam has occupied six islands in the Spratlys, Taiwan three and the Philippines has since 1971 been fortifying the seven islands. But China, which has no troops there, claims all of them, calling the group Nansha.

China also claims two other groups in the vincinity -- the Paracels (Hshisha) and Chungsha.

Apparently aware of its strategic importance, the Philippines this year acquired a squadron of F8 Crusader jets, some of which are to be based in Palawa to beef up its western defenses. Airstrips for light planes have been built on two of the islands.

The Spratlys is a group of barren, uninhabited coral atolls lying in the South China Sea between the Philippines and the Asian mainland. It has been the bone of contention for many years.

The late Chinese premier Chou Enlai as early as 1951 stated that all three groups of islands historically belong to China. During World War II Japan built naval bases on Ito Aba and some of the Spratly Islands.

After the war the scramble for the Spratlys began. The Taiwanese moved into Ito Aba in 1946. In 1965 a Filipino lawyer, Thomas Cloma, led an expedition to the Spratlys and discovered nine uninhabited islands around the Reed Bank.