Adding "active" tag to navigation list in an asp.net mvc master page

In the default asp.net mvc project, in the Site.Master file, there is a menu navigation list:

<div id="menucontainer">
    <ul id="menu">              
        <li><%= Html.ActionLink("Home", "Index", "Home")%></li>
        <li><%= Html.ActionLink("About Us", "About", "Home")%></li>
    </ul>
</div>

This renders in the browser to:

<div id="menucontainer"> 
    <ul id="menu">              
        <li><a href="/">Home</a></li> 
        <li><a href="/Home/About">About Us</a></li> 
    </ul> 
</div> 

I want to be able to dynamically set the active list item, based on the view that is being called. That is, when the user is looking at the home page, I would want the following HTML to be created:

<div id="menucontainer"> 
    <ul id="menu">              
        <li class="active"><a href="/">Home</a></li> 
        <li><a href="/Home/About">About Us</a></li> 
    </ul> 
</div> 

I would expect that the way to do this would be something like:

<div id="menucontainer">
    <ul id="menu">              
        <li <% if(actionName == "Index"){%> class="active"<%}%>><%= Html.ActionLink("Home", "Index", "Home")%></li>
        <li <% if(actionName == "About"){%> class="active"<%}%>><%= Html.ActionLink("About Us", "About", "Home")%></li>
    </ul>
</div>

The key bit here is the <% if(actionName == "Index"){%> class="active"<%}%> line. I do not know how to determine what the current actionName is.

Any suggestions on how to do this? Or, if I'm on completely the wrong track, is there a better way to do this?