More than 2,000 pages of Swiss bank records, considered crucial to the criminal investigation of the Iran-contra affair, were turned over in Switzerland yesterday to aides to independent counsel Lawrence E. Walsh.

The action ended a complicated 11-month legal battle.

The records are expected to provide Walsh's office its first direct access to the secret Swiss bank accounts used by fired National Security Council aide Lt. Col. Oliver L. North and his assistants to divert funds to the Nicaraguan contras from the sale of U.S. arms to Iran.

In a ceremony broadcast over Swiss television, Pierre Schmid, an official in the Swiss Justice Ministry, handed over the records to Robert N. Shwartz, a Walsh aide supervising the financial aspects of the probe, and two other members of Walsh's staff.

"We are delighted to receive these records," Reuter reported Shwartz as saying in a news dispatch from Berne, Switzerland. "We will review and analyze them as quickly as possible in connection with the grand jury investigation and with an eye to criminal charges."

For several months, according to informed sources, Walsh has been reluctant to seek an indictment in the main criminal case he has been assembling without the Swiss bank records. Walsh has been working on putting together a broad conspiracy case that may include such specific charges as obstruction of justice and misuse of government funds, sources said.

Sources have said that Walsh is working under the premise that the profits from the Iranian arms sales -- about $15 million -- were U.S. government funds and that it was illegal to use that money to support the contras and other operations undertaken by North's secret network.

With the aid of the Swiss bank records, Walsh's staff presumably will be able to more completely document the flow of those funds and how they were spent. "It fills a gaping hole in the evidence," one source said yesterday.

Walsh's precise prosecution strategy continues to evolve, sources said, and it is possible that the review of the Swiss bank records could force him to delay seeking his main indictment until late this year or early next year. In criminal investigations, financial records often become the source of significant new leads that investigations must run down.

Efforts to get access to the Swiss records began last December, when the U.S. Justice Department asked the Swiss government to freeze accounts tied to the Iran-contra affair. The Swiss later froze about $8 million left in the Swiss Iran-contra accounts and agreed to turn over the bank records.

But a series of legal maneuvers by some of the central figures in the Iran-contra affair resulted in the delay.

Testimony at the congressional Iran-contra hearings showed that the Swiss accounts were controlled by retired Air Force major general Richard V. Secord, North's chief assistant in the Iran-contra operations, and Albert Hakim, Secord's business partner who acted as the network's chief financial tactician.

Under a treaty with the United States, traditionally secret Swiss bank records can in some instances be turned over to U.S. authorities for criminal investigations.

However, Secord, Hakim and Manucher Ghorbanifar, an Iranian middleman, filed actions in the Swiss courts, saying that Walsh's investigation did not meet the treaty's requirement for releasing such records. The Swiss Supreme Court ruled in Walsh's favor in August.

The House and Senate Iran-contra committees obtained and made public detailed financial records on the Swiss accounts. The core of the committee's information came from records provided by Hakim, who received limited immunity from prosecution in exchange for his congressional testimony.