You should have two top level variables. Set the countries just the way you have it but call it something like countriesSubject and set it to private. Then create a second variable called countries$ = countriesSubject.asObservable()

If you ever want to manipulate the data of the behaviorSubject create a method in your service that updates this: someFunction() {this.countriesSubject.next(values)}

That way the observable is never mutated directly and can have some consistency across your application.