The State Department has asked U.S. embassies in Central America to investigate financial transactions questioned by congressional probers auditing $27 million in U.S. aid to Nicaraguan rebels, spokesman Bernard Kalb said yesterday.

His remarks came as top rebel leaders told President Reagan at the White House that renewed military aid is "desperately" needed lest future costs involve "U.S. money as well as U.S. blood." The House is scheduled to vote next week on Reagan's request for another $100 million in aid.

Kalb told reporters in response to questions that department officials would testify on the controversial aid transactions before the House Foreign Affairs subcommittee on Western Hemisphere affairs after they obtain "all of the information . . . that the department feels must be made available."

A General Accounting Office official testified last week that millions of dollars disbursed to brokers and suppliers in payment for food, clothing and other aid to the rebels, known as contras or counterrevolutionaries, had been traced to offshore banks, unidentifiable corporations and the Honduran armed forces.

Subcommittee Chairman Michael D. Barnes (D-Md.) asked the State Department to testify in response, but officials have refused on grounds the subcommittee barred the GAO from giving them all of its raw data in time to prepare adequate testimony.

"Frankly, we have to question the seriousness with which the subcommittee is conducting this line of inquiry," State Department lobbyist James W. Dyer wrote Barnes yesterday.

Kalb said U.S. embassies would "investigate some of the transactions about which questions have been raised," looking into "some receipts . . . some canceled checks, et cetera."

Speaking to reporters after meeting with Reagan, the three rebel leaders denied impropriety. Arturo Cruz, a former Nicaraguan Cabinet officer, said the United Nicaraguan Opposition (UNO) group has appointed a "blue-ribbon commission" of a lawyer, a public accountant and business administrators to "look into all the mechanisms" of the payments.

"There is absolutely no illegal situation," said another UNO director, Alfonso Robelo. The third leader, Adolfo Calero, head of the largest rebel group, said the $27 million represents less than $3 per day per rebel soldier.

Robelo said renewed military aid should include antiaircraft weaponry to counter Soviet MI24 Hind helicopter gunships, ammunition and support weapons. "We don't want anything that will escalate the war," he said.

"If this aid doesn't come in the next 30 to 60 days, we are going to suffer very high losses," Robelo added. If there is no aid, "in the future, what is going to be spent in Nicaragua is U.S. money as well as U.S. blood," he said.

Meanwhile, House Minority Leader Robert H. Michel (R-Ill.) said House passage of the full $100 million request "may be a bit too much to expect." He told reporters that efforts to draft a compromise before next week's vote "haven't collapsed" but that "it's got to happen" today.

He said Rep. Dave McCurdy (D-Okla.), a leader of the moderate bloc, has tentatively proposed providing $40 million to the rebels immediately and $60 million next February if approved by a second congressional vote.

The $40 million could include "a limited amount" of military aid after Sept. 1 if the president certifies that it is necessary to keep the rebels functioning, Michel said.

Michel said his proposal would provide $40 million immediately, including some for military use, and the rest in $20 million and $40 million chunks later. "The big stumbling block would be McCurdy's second vote," he said.

Staff writer Edward Walsh contributed to this report.