Lt. Gov. Blair Lee III, sitting in for ailing Gov. Marvin Mandel, signed into law today 425 bills including one proposed by the Marriott Corp. that will end Montgomery County's prohibition against one company owning more than one restaurant with a liquor license.

Other measures signed in the crowded Ceremonial Room at the State House today will permit Maryland drivers to turn right on red lights in 1978, require the State Board of Education to establish minimum reading standards for public schools, and add a nonvoting student member to the Prince George' County School Board.

Lee, who gets the list of approved bills from Mandel sides for his signatures, was not aware that the Marriott proposal was among them. But when he learned - after he signed if - that it was, he said, "I'm glad they got it."

Although Marriott officials say that their original proposal was meant to spur competition, the bill, passed in amended form, will benefit only Marriott, according to Del. Donald A. Roberts on, chairman of the Montgomery County House delegation.

"It was written as an anti-special interest bill," Robertson said today, "but it was heavily opposed by the restaurant association, which viewed it as a threat of competition." The bill then was amended "to placate" the fears of existing liquor license holders, Robertson said, with the "troubling" result that "only Marriott will benefit."

To qualify for a second liquor outlet in Montgomery under the new law, which goes into effect July 1, the licensee must have its principal place of business in Maryland, it must have previously held a Class B license in Montgomery County for three years, and its restaurant must seat at least 125 customers and represent a minimum capital investment of $250,000.

Robertson, who said he abstained on the bill after it was amended, said he could think of no firm other than Marriott that could meet those standards. The proposal was approved, 16 to 1, the delegation with only Del. Robert A. Jacques opposing it.

Howard J. Thomas, a Silver Spring attorney who wrote the original bill at the request of Marriott, said the amended version "could not be said to benefit only Marriott." Asked to name other possible benefactors, Thomas suggested Emersons, Ltd., of Rockville, before adding, "I'm sure there are others."

Thomas said that "as its price for support" the Montgomery County Restaurant, Hotel and Licensed Beverage Association insisted on adding provisions about the location of the corporation and that it already hold one license in the county.

Robert L. Burchette, attorney for the 100-member restaurant association, explained the association's opposition by saying that many owners of small businesses "think competition from big corporations might be more than they are able to withstand."

Thomas said enactment of the bill climaxed a four-year battle to get the proposal through the legislature, even though other areas in Maryland, including Prince George's, Baltimore and Worcester (Ocean City) counties, and Baltimore liquor licenses for years.

Lee said he will preside Monday at a hearing on bills proposed for veto by various public groups. The proceeding will be taped by the state's public broadcasting network for re-showing to Mandel at the Governor's Mansion. Mandel will make the final decision on what legislation to be vetoed, Lee said.

Among the other bills enacted with Lee's signature today were those that will:

"Increase the salary of school board members in Montgomery County whose terms begin after Dec. 1, 1978, to $7,2000 a year ($8,000 for president).

"Increase annual salaries of Orphans Court judges in Prince George's County to $12,000 ($13,500 for chief judge).

"Require landlords in Montgomery to give at least two months eviction notice to tenants who hold month-to-month leases.

"Require that real estate contracts in Montgomery and Prince George's counties disclose to the initial buyer the estimated cost of any deferred sewer and water-connections.

Permit lodges and fraternal and service clubs in Prince George's to sell liquor between noon Sunday and 2 a.m. Monday.