Ragnar said:

Need to lock content is not the whole page, but only parts of the text. 

This functionality is part of the profile where the bottom is shown to which pages people can access (when it opens access to a particular group). 

The same must be on the page with content. 

This can be done such index those pages to which it has access.

To hide a portion of the page content, try the Hide Post plugin.

Ragnar said:

The idea is to have the opportunity to display appropriate content for each of the groups in the RS. Third-party script does not give such possibility

It wouldn't be hard to modify the HidePost plugin to do that. For example, you could modify hidepost.php as follows. This will treat the hidepost number (or multiple comma-separated numbers) as permitted group IDs. In this hack, level/role requirement is not longer supported.

replace:

if ($user_level < $hidepost_max_level) {//Not meet the require level
	switch ($hidepost_max_level):
		case 0: $show = 'Subscriber';
				break;
		case 1: $show = 'Contributor';
				break;
		case 2: $show = 'Author';
				break;
		case 3:
		case 4:
		case 5:
		case 6:
		case 7: $show = 'Editor';
				break;
		case 8:
		case 9: $show = 'Administrator';
				break;
	endswitch;
	$hidepost_role_text = str_replace('%role%',$show,$hidepost_role_text);
	if ($hidepost_role_text_hide != 1) return $hidepost_role_text; else return '';
}
return $matches[2][$m_id]; //Return the content if user can see

with this:

// hack to treat HidePost number (or potentially multiple comma-separated numbers) as a permitted Role Scoper group_id
if ( $user_level == 10 )
	return $matches[2][$m_id]; // Administrators are always permitted

if ( ! empty( $current_user->groups ) )
	if ( $enabled_groups = explode( ",", str_replace('=', '', $level_tag) ) )
		foreach ( $enabled_groups as $group_id )
			if ( isset( $current_user->groups[$group_id] ) )
				return $matches[2][$m_id];

// otherwise default to not returning content
if ($hidepost_content_text_hide != 1) 
	return $hidepost_content_text;

Ragnar said:

group IDs = [WP Subscriber]

??

You can find the ID of your WP Role groups by looking at the html source of any wp-admin form which displays group checkboxes.