@Ekaterina for a generic HTML page I would indeed assume you meant the <TITLE> and <META name=description> tags. But in a Marketo context you have another title and description for every page, so it's not an "of course" situation. Given that the HTML tags are, by definition, already in the page (so their values can be copied and reused in script) asking for clarification is not unreasonable.
In the particular case of Facebook OG tags you have the problem that FB's crawler does not (at the current time) run JavaScript. Therefore if you wanted to maintain just one title/description statically, that title/description should be the OG tags section. Then flip around your concept and copy the stored OG values to the standard tags.
var title = document.createElement('TITLE');
title.innerHTML=document.querySelector('META[property="og:title"]').getAttribute('content');
var description = document.createElement('META');
description.name = 'description';
description.setAttribute('content',document.querySelector('META[property="og:description"]').getAttribute('content');
document.head.appendChild(title);
document.head.appendChild(description);