Federal
union government.
Central government
The animal that was declared as the National Heritage animal by the Central Government is the Elephant.
The Federalists supported a strong national government.
I am assuming by level, you mean level of government. There is no distinction between government on a national level and government on a federal level. The federal level of government is the highest tier of government because its central to the nation. It represents a union of states. Those union of states form a nation. So you see how the two terms are interchangable, and can be used synonymously. The federal government is government on a NATIONAL level.
National Government, Central government(as opposed to state)
In the US, the Federal Government is referred to as both a National and Central government, which has shared and separate powers with the 50 States that belong to the US.
at national or central level
at the national or central level
strong central government
You can find information about National Security on the government's national security website which posts the current threat level and additional information pertaining to national security.