MOUNTAIN VIEW, Calif.  Google is trying once again to capture some of the momentum surrounding social networking companies like Facebook and Twitter by adding new features to Gmail, its popular e-mail service.

Later this week, Google will introduce add-ons to Gmail that let users post and view messages about their day-to-day activities, according to a person at Google briefed on its plans. This simple tweak to Gmail will allow Google to mimic the status updates that have driven much of the success of Facebook and Twitter, as people return to the services again and again to check out what their friends and co-workers are doing.

To date, Google has allowed users to post only a brief message about their status through its Chat system, which is linked to Gmail. The new features would allow a more vibrant back-and-forth among Gmail users.

It is not clear whether Google will link the new Gmail features to rival social-networking services.