Upsetting a long-accepted view that nothing could rival the diamond in hardness, scientists are predicting that even harder substances may soon emerge from laboratories.
In an article being published today in the journal Science, physicists at the University of California at Berkeley disclosed their blueprint of a hypothetical substance harder than any now known.
In a telephone interview Dr. Marvin L. Cohen, who directed the research, suggested several possible ways to make the compound, which would consist of a crystalline array of carbon and nitrogen atoms.
''Materials scientists have long believed that there was something absolute about the hardness of diamond, that this ultimate in hardness could no more be exceeded than could the speed of light,'' Dr. Cohen said. ''But our calculations show otherwise. We believe it will be possible to make substances harder than any now known.'' 'New Avenues of Research'
''Aside from opening new avenues of research,'' he said, ''these substances might have very important uses in cutting and drilling tools.''
Owing to their great hardness, industrial diamonds are indispensable to many manufacturing processes, especially in machining hardened metals and ceramics. Diamond-coated wheels and drills are used to bore tunnels through rock, engrave glass and drill for oil. In these and many other applications, a material even harder than diamond would be desirable.
Dr. Cohen and Amy Y. Liu, a Berkeley student who collaborated in the discovery, based their work on predictions derived by ''first principles'' from the quantum-mechanical characteristics of the electronic bonds holding atoms together.
In crystals like diamond, the degree of hardness depends on the closeness of atoms to each other within the crystal lattice; the shorter the bonds between atoms, the harder the crystal. When carbon atoms are forced by high pressure and temperature to assume the geometric configuration of diamond, the bonds between atoms become exceptionally short. This accounts for the diamond's hardness. Shorter Electronic Bonds
The problem confronting Dr. Cohen and Ms. Liu was to devise a crystalline configuration of atoms in which the electronic bonds would be even shorter than those between carbon atoms in a diamond crystal. After considering many candidates, they realized that an existing compound, a form of silicon nitride, could serve as a model.
Silicon nitride, a very hard crystal in which silicon and nitrogen atoms are linked in a compact framework, fell short of the mark. But the two theorists calculated that if carbon atoms could be substituted for the silicon atoms in the framework and the entire structure were somewhat rearranged, bonds of exceptionally short length would result between the component atoms.
Dr. Cohen and Ms. Liu calculated that this compound could actually exist. Carbon and nitrogen atoms in the hypothetical substance, called beta-C#3N#4, would be arrayed in a continuous three-dimensional pattern suggestive of warped and distorted chickenwire. It would violate none of the rules of chemistry or physics.
''Such a crystal would be at least as hard as diamond and perhaps substantially harder,'' Dr. Cohen said. ''If it can be synthesized - and we believe it can - experimenters are likely to discover other similar configurations that would be even harder.'' High Pressure and Temperature
Dr. Cohen said that very high pressure and temperature might be needed to make such materials, but that these could be achieved by using diamond anvils - miniature presses in which two diamonds are used to squeeze substances between them to pressures comparable to those at the center of the earth.
Material under pressure in diamond anvils can be heated to very high temperatures by high-intensity laser beams passed through the transparent diamond presses, Dr. Cohen said.
Beta-C#3N#4 might also be created by bombarding diamond crystals with beams of electrically charged nitrogen atoms, he said, adding: ''The nitrogen atoms might thereby be implanted in a surface layer of the carbon lattice of the diamond, creating a very thin coating that would be harder than the diamond itself. It could be tested easily, by seeing whether it would scratch another diamond.''
The most important achievement of this work, Dr. Cohen said, has been the development of new methods for predicting the properties of substances from quantum-mechanical ''first principles.''
In another recent work based on the same type of calculation, Dr. Cohen successfully predicted the temperature at which highly compressed silicon would become a superconductor. A Computational Shortcut
Dr. Cohen said one of the main tools in his recent work was a computational shortcut that permits rapid screening of theoretical crystal models. Ordinarily, when the hardness of a crystal must be computed from the quantum-mechanical characteristics of its atomic bonds the difficult calculations entail hours of work by supercomputers.
But five years ago Dr. Cohen devised a simple formula based purely on the position of a given atom in the periodic table of the elements.
''In two seconds, using a pocket calculator, I can use this formula to obtain a good approximation of the result a supercomputer takes several hours to produce, using the normal method,'' he said.
''We now have some powerful computational tools allowing us to predict the properties of substances even before we have created them,'' Dr. Cohen added. ''As new materials proliferate, this power will be valuable for many technologies.''