The Reagan administration said yesterday it has dispatched three U.S. medical experts to Vietnam under an agreement to give that country humanitarian help and obtain information on Americans missing in the Indochina war.

The experts, including two specialists in orthopedic rehabilitation, will be in Hanoi for three days of talks beginning Tuesday, according to a State Department announcement.

They were identified as Dr. Carlton Savory of the Hughston Orthopedic Clinic in Columbus, Ga.; Fred Downs, a Veterans Administration specialist on artificial limbs, and Dr. Larry Ward, who has been involved in private relief efforts in Vietnam.

For years, the Hanoi government has been saying that its inclination to account for the 1,776 Americans still listed as missing in the Vietnam war would depend on U.S. willingness to help remedy Vietnamese problems.

During an August 1-3 meeting with Vietnamese officials in Hanoi retired general John W. Vessey Jr., acting as President Reagan's personal envoy, won a pledge of renewed assistance on the issue of those missing in action and promised to send a fact-finding team to Vietnam.

These experts, Vessey told reporters on Aug. 10, will "look into certain humanitarian concerns that the Vietnamese have that's fallout from the war in Southeast Asia."