Insert code into <head> using ASP.NET

I have some code that looks something like this:

<head runat="server">
  <script type="text/javascript">
     var params = {};
     params.param1 = 'value1';
     params.param2 = 'value2';
     params.param3 = 'value3';
     params.param4 = ''; // ASP.NET value 1
     params.param5 = ''; // ASP.NET value 2
     function.call(params);
  </script>
</head>

How do I use ASP.NET to populate param4 and param5? I've read about master pages and content placeholders, but is there a way that I can just do something like params.param4 = '<%= var1 %>'; or params.param4 = '<asp:var />';?

Edit

Thanks to everyone who answered so quickly. I must have had a parsing error or something that made me think this wasn't possible. Just to make it clear what I did to solve my problem:

ASPX page:

<head>
  <script type="text/javascript">
     var params = {};
     params.param1 = 'value1';
     params.param2 = 'value2';
     params.param3 = 'value3';
     params.param4 = '<%= var1 %>';
     params.param5 = '<%= var2 %>';
     function.call(params);
  </script>
</head>

CS Code-Behind:

public string var1 { get; set; }

public string var2 { get; set; }

protected void Page_Load(object sender, EventArgs e)
{
   // setup code goes here
   var1 = 'param4';
   var2 = 'param5';
}

Note: You don't need runat="server" in the head, and just as long as the variables are public in the code-behind, they can be accessed via <%= %> in the <head>.

Solution

You sort of answered your own question. You can declare your variables in the code-behind and then use them in your code with <%= %> tags, or you can use the RegisterClientScriptBlock method to add the JavaScript to your page on the fly.