Tomales is the little town that can, officials said in announcing Novato National Bank's plans to open a branch office there and stop the town from being without a bank. The 3-year-old financial institution with assets of about $50 million will take over the old Bank of America branch that had served the western Marin County town of about 270 for more than 50 years. The historic building--complete with old-fashioned teller windows and marble counters--was purchased by local investors earlier this year. Bank of America pulled out of Tomales in November, 1985, and community leaders since then have been trying to attract another bank to the community. The bank's pullout "was a real slap in the face," said Sally Parks, owner of a local delicatessen. The move forced residents to drive about 32 miles round trip to Petaluma to do their banking.