TOKYO (Reuters) - Japan's Olympus Corp and Matsushita announced a new digital camera format on Tuesday that will make single lens reflex (SLR) models smaller and lighter, in a bid to drive sales of their advanced machines.

SLR cameras, which are high-end models with interchangeable lenses, are the most lucrative and fastest growing segment of the overall digital camera market.

But some compact digital camera users are reluctant to move up to SLR models because they are bulkier and heavier.

The new format, called the Micro Four Thirds System, would make digital SLR cameras thinner and lens units smaller than those based on the existing Four Thirds System.

The Four Thirds System is an open standard that specifies the size of the imaging sensor and lens mount, ensuring compatibility of lenses between products.

Olympus and Matsushita Electric Industrial Co Ltd, maker of Panasonic brand electronics, offer digital SLR cameras based on the Four Thirds standard, while Sigma Corp makes Four Thirds-based lenses.

"Packing high picture quality into a body thin enough to slide into a pocket. That is the basic concept of Micro Four Thirds," Haruo Ogawa, head of Olympus Imaging Corp's SLR business division, told a news conference.

Olympus Imaging is Olympus Corp's digital camera subsidiary.

Matsushita and Olympus did not disclose the actual size or design of their new cameras based on the new standard, and declined to comment on prices and launch timing.

Olympus is the world's fourth-largest digital SLR camera maker behind Canon Inc, Nikon Corp and Sony Corp. Matsushita ranks sixth.

(Reporting by Kiyoshi Takenaka; Editing by Michael Watson)