Yes, projects Sigma and Plato are programs that (allegedly) are in charge of communications with extraterrestrials.
Project Sigma: http://www.exopaedia.org/Sigma+Project
Project Sigma is the name of the project that deals with contact and communication with alien civilizations. It is believed that it started under Pres. Eisenhower.
Bill Cooper claimed SIGMA is the project which first established communications with the aliens and is still responsible for communications. This first official contact would have been made in 1953. Like in the movie "independance day," huge ships were detected in orbit, and contact was made. This would lead to project Plato and to project Serpo (the exchange of ambassadors).
Information that allegedly was leaked from the Pentagon and published on the Serpo site (
www.serpo.org) in August 2006, however, claims project Sigma is an ongoing project that involves the studying of alien spacecraft.
Note: as all other sources refer to Sigma as the communications' programme, I have serious doubts that Sigma would be the name of the project that involves studying alien spacecraft. (See: Redlight, Snowbird & Pluto).
Project Plato: http://www.exopaedia.org/Plato+Project
According to MW Cooper, PLATO is the name of the project responsible for diplomatic relations with the aliens.
It is related to project Sigma, which is the central project that is in charge of communications with the aliens.
Project Plato was created in 1953 when through Sigma contact was first made with alien spacecraft orbiting the planet.
On Feb. 20, 1954, Project Plato secured a formal treaty (illegal under the US Constitution) with the aliens. The terms were that the aliens would provide the US government with technology. In return the US agreed to keep their presence on earth a secret, not to interfere in any way with their actions, and to allow them to abduct humans and animals. The aliens agreed to furnish MJ- 12 with a list of abductees on a periodic basis. (See: Preserve Destiny Project)
According to Val. Valerian this treaty was renewed, again within the Plato framework, on 25 April 1964, at Holloman AFB, New Mexico. It is possible that this resulted in the exchange, from 1965 until 1978, of ambassadors, under the project Crystal Knight. (See also 'Serpo').