Joint U.S.-Egyptian military exercises began here today, but Egypt imposed a news blackout because of the political sensitivity of its military ties with the United States.

The exercises, scheduled to last about a month, are in the preparatory stage, well-informed sources said. The actual naval and air maneuvers, involving 5,500 U.S. troops and advanced U.S military and communications equipment, including Airborne Warning And Control System (AWACS) observation planes, will take place during the second and third weeks, the sources said.

This year's exercises, named Bright Star 83, are the most sophisticated and elaborate since the two countries began staging joint maneuvers three years ago. Similar, but smaller, joint operations to test the ability of local armies to coordinate with U.S. troops in the event of a threat to friendly governments in the region are taking place simultaneously in Sudan, Somalia and Oman.

The Egyptian government seemed to be concerned about the possible domestic and international repercussions of an American show of strength on its territory.

Reflecting its interest in maintaining the image of a leading independent, nonaligned Arab country, Egypt canceled joint maneuvers planned for last year following Israel's invasion of Lebanon, which caused a surge of anti-American feeling in the Arab world. Similar considerations have led to the imposition of a total blackout here on coverage of the Bright Star 1983 exercises.

The Egyptian government's sensitivity also threatens to delay completion of construction work on the Ras Banas air base beyond the 1986-87 deadline previously set for it. President Hosni Mubarak has reaffirmed in writing Egypt's commitment to offer the United States facilities in Egypt, an official involved in the talks said, but differences stemming from Egyptian feelings have marred the talks, which were suspended last spring.