In the wake of House embarrassment over members' use of official expenses accounts to buy liquor, flowers and spot television announcements, senators have been warned to limit use of their funds "strictly to official business" and "avoid any expenditures which could be characterized as 'personal promotion.'"

In an unusual "Dear Colleague" letter, Chairman Walter (Dee) Huddleston (D-Ky.) of the Senate Appropriations Subcommittee on the Legislative Branch and its ranking minority member, Sen. Richard S. Schweiker (R-Pa.), cautioned members "to monitor closely" their recently expanded and liberalized expense allowances "to assure that there is no abuse . . ."

Huddleston wrote that his subcommittee staff, the Rules Committee and the Senate leadership are working on guidelines "as to what constitutes 'official business.'"

It was learned that one of those urging caution in use of the new allowance is Sen. Howard Cannon (D-Nev.), chairman of the Rules Committee, which has responsibility for approving all expense vouchers. According to one source, that committee has yet to see anything (unusual," but Cannon wants written guidelines, to be certain "nothing improper" comes to his committee for reimbursement.

In a little-noticed action last summer, the Senate voted to increase the expense allowances by 10 per cent and to liberalize the rules to permit the money to be used for "expenses as the senator determines are necessary."

Senate-wide, the increase could come to $500,000 for a full year, depending on how many members use the entire amount available to them. Last year, according to testimony before a Senate committee, 21 members used their full allowances.

Each senator's allowance depends on his state's population and its distance from Washington. The yearly amount available in the newly created open expense account ranges from $3,000 for a senator from Delaware to $13,000 for a senator from Hawaii, according to figures supplied by the Senate Appropriations Committee.

The new open allowance was developed to replace unofficial office accounts which many senators had maintained with funds contributed from institutions and organizations. Those accounts were effectively eliminated by ethics reform rules adopted by the Senate earlier this year.

Now senators may maintain surplus campaign fund accounts, but they must be used for political expenditures - not for items considered official expenses.

In establishing the new fund, some 56 senators petitioned Huddleston's subcommittee requesting an account which would give members "the right . . . to determine their necessary business expenses . . ."

Initially, according to the Senate Appropriations Committee report, the money could be used for expenses in running a senator's Washington office, including transportation around the city."

A member was prohibited, according to a recent letter from the Senate Disbursing Office, from using the allowance for "entertainment or meals" in Washington.

The legislation that established the new open allowance required that each voucher from that account be published in a separate section of the printed report of the Secretary of the Senate.

It was disclosure of questionable expenditures by House members as printed in the Clerk of the House report that led to the House Administration Committee's establishment this month of new rules on use of their official office accounts.

The Senate portion of the Legislation Branch appropriations bill, passed last July, carried other items that were not widely reported:

The amount expected to be spent by members and Senate staffers on foreign travel was increased by 50 per cent - growing from $500,000 in fiscal 1977 to $750,000 in the current year.

Each member was allowed two WATS telephone lines without charge to his telephone allowance. Previously, a WATS line, which permits unlimited calls to a specific part of the country, used up half of a member's telephone allowance.

Senators and their staffers were permitted reimbursement of up to $35 per diem and travel expenses for trips anywhere in the United States if they are on official business. Previously they could only be reimbused for travel to the member's home stote.