Deposed president Ferdinand Marcos, increasingly beleaguered by efforts of the new Philippine government to recover what it calls his "ill-gotten" wealth, fell victim to his own penchant for secrecy last month when Swiss banks frustrated attempts to withdraw his assets, a government investigator said today.

Contradicting Marcos' denial that he and his family have stashed millions of dollars in Swiss bank accounts, Steve Salonga, an investigator on the Presidential Commission on Good Government, said documents showed that Marcos secretly opened his first Swiss account in 1967 during his first term as president. He said the commission's latest documentation on Marcos' Swiss accounts was dated December 1985.

The initial Swiss account, opened with a deposit of $1 million, "blossomed over the years into 12 to 15 accounts, none of which has a balance of less than $1 million," Salonga said. He estimated that the total value of the accounts is "well over $100 million," but backed away from an earlier statement by a commission member who said Marcos had stashed $800 million in a Swiss bank.

Salonga, a lawyer whose father, Jovito Salonga, heads the presidential commission, said Swiss banks surprised the Philippine investigators when they unexpectedly "resisted" efforts to withdraw funds from Marcos' accounts by not acting immediately on telexed instructions to the banks. Commissioner Raul Daza confirmed last week that efforts to withdraw the funds had led the Swiss government to impose a freeze on Marcos' assets held in Switzerland.

According to government and diplomatic sources, the cooperation given to the commission so far by various governments appears to reflect the unusual degree of international good will that has greeted the new administration of President Corazon Aquino, which came to power in a relatively peaceful "revolution" in February. The cooperation in recovering allegedly stolen assets has far exceeded that extended to Iran after the February 1979 revolution against the late shah, for example.

Salonga said the Swiss bankers were able to stall on instructions to withdraw Marcos' assets because of the complicated procedures adopted by the former president to keep the accounts secret and disguise their ownership. He said Marcos used fronts and fictitious names that changed from month to month in transactions with the banks, in which Marcos held stock, commodities, cash and silver and gold bullion accounts. He said a coding system was used for telex instructions in which a given month of the year had to match a special code name.

"Unless the name and the month matched, the telex was disregarded," Salonga said. He said the first and last names of different international film stars often were combined to produce the fictitious names.

"All it takes is two or three lines in a telex, and that's it; the whole thing can be gone," Salonga said of the efforts to withdraw the Swiss assets. However, "the very ambiguity and anonymity of the instructions gave bankers a lot of discretion," Salonga said, and the bankers apparently used it to delay action on the withdrawals. He had no further explanation for the banks' response, but indicated that he believed there was sympathy in Switzerland for the Philippine government's efforts to recover Marcos' wealth.

"The attitude of the Swiss government was the most unexpected thing," Salonga said. "None of our research means anything without the cooperation of governments. It's refreshing." He added that the commission sought to use diplomacy where possible, rather than litigation, to pave the way for recovery of Marcos' assets.

Salonga and two other commissioners, Pedro Yap and Ramon Diaz, are scheduled to arrive here Wednesday from trips to the United States and Europe. They have been seeking evidence on Marcos' holdings and taking steps to recover them.