A federal grand jury in Alexandria has been investigating possible fraud and illegal payments to high-ranking Philippine officials in connection with Pentagon-financed military purchases, according to individuals familiar with the investigation.

The investigation, begun more than a year ago, at first centered on a California company called Amworld, which won a $17 million contract from the Philippines in 1983 to supply microwave communications equipment to its armed forces, the sources said.

Financing for the contract was approved by the Defense Security Assistance Agency under the Pentagon's foreign military sales program. After an initial payment of $6 million, the Pentagon refused to release any more funds for the project and initiated an internal investigation, sources said. Its findings were later turned over to the grand jury.

The grand jury was at first looking into "allegations of overpricing . . . and fraud in obtaining the contracts. And they are looking at [violations] of the Foreign Corrupt Practices Act," said one source familiar with the investigation.

"We're confident that Amworld will be cleared of any wrongdoing," said Anne Fraser, an attorney for the company. Amworld was incorporated in Brisbane, Calif., in 1981 and is now owned by a Hong Kong corporation called Golden Assets Ltd., according to sources.

A company that had a subcontract with Amworld to install the equipment in the Philippines is also under investigation, a source said. The company was identified by the source as the Philippines-based Electronic Specialists Inc., owned by Filipino businessman Raymond Moreno.

"I think this investigation is a result of a political and diplomatic intrigue," said Moreno's attorney, Thomas A. Wadden. "A thorough investigation is going to establish that [Moreno's] company has not violated any U.S. or Philippines' laws."

The New York Times reported yesterday that the United States wanted to use information unearthed in the investigation to persuade Philippines' President Ferdinand Marcos not to reinstate Gen. Fabian Ver as chief of the armed forces, but federal prosecutors declined to reveal details, citing grand jury secrecy rules.

The Philippine Embassy did not return a reporter's phone call.

The grand jury investigation has widened in recent months to include other Pentagon-financed contracts that provided military equipment to the Philippines, according to one source. The New York Times identified one of the companies involved as the Sikorsky Co.

Robert Stangarone, a spokesman for the Sikorsky Co., said he was aware of the investigation, but said that "Sikorsky has not been notified or subpoenaed or asked to provide information to the grand jury."

Stangarone said that in 1983 the company sold 19 helicopters to the Philippines government for $63 million that was financed by the foreign military sales program. He said Sikorsky retained a Philippine company called Detech to provide administrative and marketing services at that time. "All payments we made to Detech were in total compliance with U.S. law," Stangarone said.

Last July, United Press International reported that Philippines Defense Minister Juan Ponce Enrile had ordered an investigation into Amworld's $17 million contract to provide the communications equipment needed by the armed forces, which are fighting an insurgency.