A GREAT read in th 80's. Help me back!

[Jfarm64]

I was a visiting Registrar at the hospital in Gloucester. I borrowed a book from their library which I'd love to find. All I recall is the plot: Earth's scientists detect a massive alien invasion force headed our way. They are escaping their own dying planet. Proof comes when alien scout ships are discovered at the lagrangian point behind the moon as well as in our oceans. Nations band together to construct a massive gamma ray weapon to fry the aliens from a gazillion miles away. A great read.

 

[jastius]

this probably isn't it but it sounds similar

The Killing Star by Charles Pelligrino and George Zebrowski

 

[CassFrank]

This sounds like Albert and David Hill’s Invader (1980). The weapon the world devises is called a Gaser - gravity laser.