Indian Prime Minister Charan Singh completed the first phase in the formation of his shaky coalition government today as another 17 ministers were sworn in.

The government is now 26 strong, 19 of whom have Cabinet rank, but there is the growing unease in political circles about the minority government's ability to survive a parliamentary confidence vote scheduled for late in August. These fears were not allayed today by brave words from the paticipants at the swearing in ceremony.

The new foreign affairs minister, Shyam Mishra, said the government would be able to give an impressive account of itself within a hundred days, when the people would "be able to compare our performance" and feel the difference.

He said that for the first time, there were three Moslems in the central Cabinet and that other minority communities also were given representation.

Many in Delhi wonder whether the government will be able to survive a hundred days, however. The Indira Congress Party of former prime minister Indra Gandhi is throwing a long shadow on the political scene. With its 71 parliamentary seats, the Indra Congress may yet hold the fate of the Charan Singh administration.

The major appointment today was that of C. Subramanian, 69, as defense minister. Subramanian, was born in the southern Indian state of Tamil Nadu, and was at one time chairman of the committee on the aeronautics industry. Immediately after the swearing in ceremony, he went to his office in the Defence Ministry to meet the three service chiefs for a review of the security situation on the subcontinent, ad the latest developments in India's defense equipment production industry. India is the biggest manufacturer of armaments in the third world.

In addition to Singh, the cabinet includes nine members of the Janata (Secular) Party, eight from the Official Congress and one Socialist. Five of eight menisters of state come from t Janata (Secular) and the others from the official Congress.

All but four of the 27 ministers appointed so far have had previous ministerial experiance, eight Congress members having served under Gandhi during her 21-month emergency rule before the Congress Party split.

Thirteen of the ministers served under prime minister Morarji Desai before the revolt against his leadership.