Maryland Gov. Harry Hughes vetoed yesterday a bill that would have allowed state judges to order the suspension of driving privileges for teenagers convicted of violating the state's drinking laws, a measure passed to combat underage drinking.

"Techically, [the legislation] needs some more work," said Judson P. Garrett, Hughes' legislative counsel. The chief flaw in Hughes' opinion was the provision allowing youths charged with drinking violations to be prosecuted in their home counties.

"That provision would be a colossal nightmare for Ocean City," the Eastern Shore resort where alcohol-related offenses are a perennial summer problem, Garett said. The logistical programs of having policemen travel to teen-agers' home counties for trials would have effectively eliminated any enforcement of the law, he added.

The bill was one of 30 Hughes vetoed yesterday on the final day of billsigning for legislation passed by the 1980 General Assembly.

Among the bills signed by Hughes yesterday was one that raises the ceiling on interest rates for most consumer loans and some credit card accounts. Last week, two legislators who had fought the interest-rate measure during the session argued that the recent decline in prime interest rates had nullified bankers' arguments that existing ceilings gave them no margin for profit and thus no incentive to make loans.

But Hughes said yesterday he was not convinced that interest rates had declined enough to make the measure superfluous. "I know the prime rate is coming down," he said, "but a lot of states have interest rates higher than Maryland's, and Virginia has no limit."

The measure, sponsored and supported by legislators who enjoyed the hospitiality of the Maryland Bankers' Association at a convention in Boca Raton, Fla., last spring, would permit banks to charge 18 percent interest on credit card blances up to $700, after which they may charge only 12 percent. The existing cutoff point is $500.

In addition, all consumer loans from car loans to home improvements loans -- may command an 18 percent interest rate after July 1 as a result of the legislation. Currently, bankers may charge only 12 percent for loans of more than $3,500.

Hughes also signed legislation banning the sale of drug paraphernalia in Maryland after being advised by the attorney general's office that the measure was constitutional.

The teen-age drinking measure, introduced late in the three-month session and passed 10 minutes before the legislature finished its business in April, was designed as a broad-based effort to decriminalize many of the state's drinking laws.

Its passage by the key House Judiciary Committee in late March effectively deflated the effort to raise from 18 to 19 the state's minimum drinking age, an effort that had won considerable support after a traffic accident killed 10 teen-agers last spring.

But as soon as the legislature adjourned, the opposition to the bill coalesced, as juvenile-law experts joined Baltimore City policemen in arguing that the bill was riddled with technical flaws and would make it more difficult -- not easier -- to curb teen-age drinking.