A National Park Service executive told a congressional subcommittee today that she violated federal guidelines when she allowed Interior Secretary James G. Watt to dip into a private fund to pay for two controversial Christmas parties he gave at Arlington House, or the Custis-Lee Mansion.

Nancy C. Garrett, an associate director of park service, told the House Interior Oversight subcommittee that she decided not to seek the required signatures for disbursal of funds because Watt's office had already decided to use the money.

Garrett also testified that she sent a memo to her Interior Department superiors advising them of the guidelines, but did not question the expenditures further. "I did not believe anything was to be gained by it," she said.

Earlier this week the General Accounting Office held that Watt improperly diverted almost $9,000 in funds to pay for the two parties held at the mansion, which is operated by the park service and overlooks Arlington National Cemetery. The GAO said that Watt, or the "Interior officials who authorized the expenditures," must repay expenses that cannot be charged to Watt's government entertainment fund. That amount is estimated by the GAO to be about $4,500.

Watt has maintained that he was justified in financing the parties with funds from a park service fund composed of private donations intended for park-service-related projects.

Watt was invited to testify before the subcommittee yesterday, but declined, saying he did not wish to be involved in a "media sideshow." Instead, he sent a raft of Interior and park service employes, including, Richard Hite, the department's deputy assistant secretary. Hite has taken responsibility for deciding that the voluntary donations fund could be used to pay for Watt's parties.

Yesterday, after persistent questioning by subcommittee Chairman Edward J. Markey (D-Mass.), Hite acknowledged that Watt would be responsible for any repayment to the government.