Best way to convert .html to .php on a few pages without hurting rankings?

I need some features on about 50 similar pages on a site, we are thinking of converting them to .php. What is the best way to do this without hurting rankings?

The pages rank well for their specific keywords....

Would some type of like 301 redirect work, or leave .html and try to direct from that?

Any ideas?

Thanks

 

I think we can do that using .htaccess ..but i think it will effect your rankings

 

If you only need a few modules, you can let the server read php on an html url without too much hassle, Look for this in the programming section of the forum.