Museum officials in Washington and their lobbyists expect President Reagan to request immediate as well as future funding cutbacks in the budget of the Institute for Museum Services that will shut down its grant-making operation.

"We have learned that the administration will propose the complete rescission of current fiscal 1982 funds for the Institute for Museum Services and no funds for IMS in fiscal 1983," reads a Jan. 25 memo from the American Association of Museums that was sent to more than 150 museum directors around the country.

"We are both shocked and disturbed by the administration's intention to eliminate the institute," continues the memo from the association's director, Lawrence Reger, and its legislative counsel, Peter Kyros. "We were optimistic that the institute's move from the Department of Education to independent status as sister agency to NEA and NEH, as well as the confirmation of Lilla Tower as the new director, would assure IMS of administration support for fiscal 1983 and the maintenance of hard-won fiscal '82 appropriation. Clearly, our optimism was misplaced."

Lilla Tower, the director of the IMS, refused to answer a reporter's repeated inquiries yesterday. "She has incessant meetings," said IMS staffer Roberta Faul, speaking for Tower, "and after the president's budget message she'll be happy to talk to you." The budget message is to be sent to Congress Feb. 8.

Tower, an attorney and the wife of Sen. John Tower (R-Tex.), was nominated last year for the position after IMS had weathered a similar administration attempt to "zero out" the agency. Despite that request, Congress appropriated $11.5 million for IMS, and that bill was signed by President Reagan on Dec. 23 -- barely a month before word of a planned rescission of those funds.

The IMS funds a variety of small and large museums, and considers some zoos to be within its purview. Unlike the National Endowments for the Arts and the Humanities, the IMS contributes funds to the general operating support of museums throughout the country.

IMS funds have become crucial to museums, according to Craig C. Black, the director of the Carnegie Museum of Natural History in Pittsburgh and the chairman of the board of the American Association of Museums. "We just can't make that up at the gate," said Black yesterday.

In many cases, museums with good funding track records expect to get funds for fiscal 1982. "Budgets have been prepared," Black said. "Museums have made certain plans based on those budgets. To wipe it out would cause a great deal of hardship for small as well as large institutions. And fund-raising at the corporate level is difficult these days."

Said one museum director who is expecting $34,000 from the IMS this fiscal year, "That's already been budgeted."

Black said that based on his "various sources, I'm convinced that President Reagan will ask for a rescission, but I'm not convinced he'll get it."

"Members of the museum community will make the quality of the programs clear to their representatives in the House and the Senate," said Maureen Robinson, legislative coordinator for the American Association of Museums. "Last year, that was done through personal phone calls and letters."

Whatever the February budget message holds for the IMS, it's probably too late for people to lobby against it at the White House level. "It's all locked up," said Edwin Dale, assistant director for public affairs at the Office of Management and Budget, about the president's budget proposal. "It is too late to change anything on the outlay side."