Maryland Gov. Harry Hughes yesterday vetoed legislation that would have eliminated the current requirement that landlords give tenants 180 days' notice before converting any vacant apartment in their buildings to condominiums.

The measure, which had been opposed vigorouslby Montgomery County officials, could have "severely dislocated many citizens," particularly in light of the existing shortage of low and moderate-income housing in Montgomery, the governor said.

In his veto message, Hughes refused to rule out the "merit" of the measure, but said that the county government and Mongomery tenants need a year to prepare for its impact.

In the past five years, 6,730 of the county's approximately 57,000 apartments have been converted to condominiums. The County Council recently defeated a measure that would have put a 90-day moratorium on condominium conversions.

Hughes also vetoed a controversial bill that would have permitted juvenile delinquents at least 16 years old to be sentenced to as much as two weeks in a special section of the Prince George's County jail.

The bill was inspired by a controversy that began when Prince George's County Circuit Court Judge Vincent J. Femia began sentencing juveniles to such terms despite a state law that prohibits sending youthful offenders to adult prisons.

In his veto message, Hughes cited a letter from the Law Enforcement Assistance Administration that said the county jail was "seriously over-crowded and understaffed" and that the juveniles there could not be separated from adult inmates or adequately protected.

Jailing of the juveniles in the county facility could make the state ineligible for some federal law enforcement funds, the letter said.

The vetos of these two measures came as Hughes signed a total of 329 bills passed during the 1979 state legislative session. Yesterday was the veto deadline. Any legislation not vetoed would have gone into effect, with or without Hughes' signature.

Included in the legislation signed yesterday were measures to allow anyone over 18 to ride a motorcycle without wearing a helmet and to allow the storage of nuclear wastes at the Calvert Cliffs plant for another year.

Opponents of the nuclear waste storage measure are collecting signatures to make it subject to a referendum. No referendum could be held on the issue until the 1980 election, so a successful petition drive would block the measure for at least 18 months.

Regardless of the result of the petition drive, however, the waste must remain at the Calvert Cliffs facility because there are no other available storage sites in the country.