Soviet authorities have increased the seriousness of their charge against imprisoned dissident leader Yuri Orlov, dissident sources said yesterday.

Orlov, a founder of the Moscow-based Helsinki human rights monitoring group has been charged with anti-Soviet agitation and propaganda, which carries a possible seven-year prison penalty the sources said. The earlier charge, spreading anti-Soviet fabrications, carries a maximum penalty of three years.

This is the latest of the Kremlin's moves against the human rights activities here and in other cities.

orlov, 52. a nuclear physicist, was seized and jailed almost a year ago and has been denied any contact with family or friends since. His arrest was made an issue by the White House, reportedly infuriating Soviet President Leonid Brezhnev.

The Kremlin has shown no inclination to lessen its pressure on the dissidents and Carter has substantially oftened his public gestures on behalf of the activists.

Orlov founded the Helsinki monitoring group in May 1976, with about a dozen other persons, to check Soviet compliance with the human rights pledges contained in 1975 Helsinki agreement on European security and cooperation. The group issued numerous reports alleging violations of the human freedoms provisions.

Other dissidents imprisoned since then include Anatoli Scharansky and Alexander Ginsberg, whose detentions have brought criticism from the West. Other activists have been frightened into silence by the Soviet secret police or involuntarily deported.

Sources told Western correspondents yesterday that Orlov's wife, Irina, had been summoned to Lubyanka Prison and informed of the new charge. She also was told to find a Soviet lawyer for her husband within five days, sources said. Shew has been trying to obtain the services of a British lawyer. Soviet authorities recently refused to allow a foreign lawyer to defend Scharansky.

Irine Orlov reportedly was told that the investigation of her husband is nearly completed. Soviet law allows the defense to begin preparing its case only after the prosecution case is concluded so this does not definitely indicate that a trial is near. Scharansky, for example, has been extended in the pre-trial investigation process an additional six months.

The new charge against Orlov, carries a full penalty of six months to five years in a labor camp, plus internal exile of up to five years or up to five years exile alone.