If the government takes over freddie and fannie mac, will the stock be worthless?

Yes, the stock will go to zero

The government is unlikely to take them over. After the bailout was announced, the stock jumped.

marina, you are wrong, and a simple Google of this topic will illuminate the reality of insolvency at both Fannie and Freddie.

The stock jumped as a result of SEC banning shorting of 19 financial stocks, the two mentioned above included.

Fannie and Freddie will be taken over in the very near future, as they are insolvent and do not have enough finanical reserves in relation to the number of defaulted loans in the portfolio.