The United States yesterday rejected Soviet President Leonid Brezhnev's proposals for demilitarization of the Persian Gulf, calling them "vague, inequitable and unworkable in practice."

A strongly worded State Department statement, made public by spokesman Jack Cannon, called it "ironic" that Brezhnev should make such proposals "when the continuing Soviet invasion of Afghanistan is obviously the chief threat to the security of the region."

U.S. officials said informally that they considered Brezhnev's proposals, announced Wednesday during his visit to India, a propaganda gambit rather than a serious bid for negotiations and agreements. Among the purposes of the Soviet attempt, in this view, were desire to capitalize on neutralism in the Persian Gulf, to draw attention away from Afghanistan and to take a peaceful-sounding position amid the apprehension about a possible Soviet invasion of Poland.

Brezhnev proposed that the United States and other Western powers, plus China and Japan, agree not to set up foreign military bases in the Persian Gulf area, not to use or threaten the use of force against the countries of the area, to respect these nations' nonaligned status and their sovereign right to their natural resources, and not to raise obstacles or threats to the use of sea lanes in the area.

The general tenor of several of the Brezhnev proposals is similar to announced policies of the Carter administration. The proposals would seem to conflict, however, with the administration's drive to improve its access to military facilities in Oman, Kenya and Somalia as part of a buildup of U.S. military forces in the region.

Even if it were so inclined, officials pointed out, the Carter administration, in its waning days in power, is in no position to open serious discussions with the Soviets on this subject.