Federal occupational health officials said yesterday they have uncovered widespread neurological and psychological problems among workers who handled the pesticide leptophos at a plant owned by the Velsicol Chemical Co. in Houston.

Officials of the National Institute for Occupational Safety and Health also charged during a Senate subcommittee hearing that Velsicol withheld vital information from federal inspectors about health problems the company's leptophos workers were having.

The Chicago-based chemical company was indicted Monday by a federal grand jury on charges in an unrelated case that it concealed laboratory test results from the Environmental Protection Agency that indicated that two of its best-selling pesticides might cause cancer.

A Velsicol spokesman yesterday said he was not prepared to comment on the NIOSH testimony on leptophos. He said, however, that the chemical company's policy was to cooperate fully with federal health inspectors.

Velsicol's problems were further compounded during the hearing yesterday on pesticide control before the Senate Subcommittee on Agricultural Research and General Legislation. NIOSH officials told subcommittee Chairman Patrick J. Leahy (D-Vt.) that they recently learned of still more health problems among workers exposed to the pesticide DBCP at Velsicol's Eldorado, Ark., plant.

Dr. Channing Myer, an official of the NIOSH hazard evaluation and technical assistance branch, said he received preliminary information from the company that about half of a group of 24 workers who handled DBCP at the Arkansas plant showed abnormally low sperm counts in medical examinations.

DBCP is a pesticide which has been widely used on fruit and vegetable crops to kill worms and other soil insects. Last July DBCP-manufacturing workers were reported to have been made sterile by the chemical at the Occidental Chemical Co's plant in Lathrop, Calif., and Dow Chemical Co's DBCP plant is Magnolia, Ark.

Velsicol's spokesman said yesterday that his company manufactured the pesticide at Eldorado, Ark., plant for two months in 1975. He said the company's report of low sperm counts among the Eldorado workers was part of a study which he called "inconclusive and still going on."

Dow officials announced yesterday that some of the workers at their Magnolia plant who had been made sterile by DBCP appeared to be regaining their fertility. The company announced "significant" improvements in sperm counts in seven of 47 pesticide workers whose counts last summer were at or near zero.

However, yesterday some doubt was cast upon the Dow results by NIOSH officials, who said Dow was using a standard of 20 million sperms per cubic centimeter as a "normal" reading. The NIOSH officials said the Dow standard was low and that a "normal" sperm count should be about 40 million sperm per cubic centimeter.

Testifying before the Senate subcommittee yesterday on leptophos, Dr. Bobby Craft, director of the NIOSH division of surveillance, hazard evaluation and field studies, said that among 155 Velsicol workers tested from the company's Bayport plant in Houston 63 showed abnormalities.

The tests included nerve and muscle functions as well as psychological examinations to determine performance in thinking, perceiving and carrying out certain simple tasks. Eleven of the workers showed nerve and reflex problems, while the rest had a wide variety of psychological problems, Craft said.

Dr. Charles Nintaras, NIOSH's leptophos project coordinator, said the abnormalities found in the medical tests were "significantly higher" than those found among a similar group not exposed to the chemical.

Craft said that during a visit by NIOSH investigators to the Bayport plant in February, 1976, the NIOSH officials found that two of 26 persons showed mild neurological problems.

"What we did not know at the time was that at least 12 cases of serious neurological disorders had been identified in June of 1975 by a medical consultant to the company's" Craft said. NIOSH was not informed of the additional cases by the company, and only learned of them from another government agency in September of last year, he said.

"When we went there they had information, they didn't share with us, even though we asked for it," Craft said. Once the full investigation was launched by NIOSH, however, Craft said Velsicol cooperated in helping find former employees from the plant.