PARIS -- In bold, daytime operations, thieves cut two paintings from their frames at two Paris museums yesterday, one a Renoir stolen from the Louvre, Museum of France officials said.

Both paintings, Renoir's "Portrait of a Seated Woman" and Ernest Hebert's "Portrait of Monaluccia," were small-format paintings. Such paintings are often chosen by thieves because they can be easily concealed.

The theft of the Renoir, which had been hanging in the Louvre's third-floor Pavillon de Flore gallery, was discovered about 2:15 p.m., officials said. The Hebert was discovered missing from the Ernest Hebert Museum, across the Seine River on the Left Bank, about an hour later. Officials said both paintings were stolen during the day, presumably after the museums had opened.

Officials noted that in both cases the paintings had been cut from their frames, but could not immediately say whether the thefts were related.

"Portrait of a Seated Woman," painted between 1916-1918, measures 13 1/2 by 10 1/2 inches. Hebert's work, painted around 1870, measures 14 3/4 by 12 3/4 inches.

A catalogue of stolen paintings, recently published by the Interior Ministry, shows that small-format paintings are the most common targets.

The catalogue also shows that 58 percent of the paintings stolen from French museums between 1979 and 1989 were taken from the stocks. About 40 percent of the stolen paintings had been on display.

The last Paris museum theft that occurred during the day was in 1985, when a gang of armed thieves held up the Marmottan Museum, stealing a number of impressionist works, including Claude Monet's "Impression Sunrise," which inspired the name for the impressionist movement.

The painting has not been recovered.