Montgomery County officials announced plans yesterday that will require residents in two out of three homes throughout Montgomery to separate newspapers from trash for special curbside collection.

Starting July 2, all residents in single-family homes and town houses, except those who live in Montgomery's incorporated municipalities, will have to bag or bundle newspapers for recycling.

The expansion of the program will mean that about 155,000 households, or two-thirds of those in the county, will be recycling newsprint. Curbside collection of newspapers has been available for more than 10 years to 80,000 homes in the lower, eastern part of the county, including Silver Spring, Bethesda and some neighborhoods outside the city of Rockville. Towns and cities in the county set their own recycling goals.

"This is just the start," vowed County Executive Sidney Kramer, who also announced the beginning of yard-waste collection for 55,000 homes in the midcounty area.

Fairfax County and the District of Columbia already require residents to separate newspapers for recycling, while Prince George's County is phasing in a program and Arlington has a voluntary program, according to the Metropolitan Washington Council of Governments.

Montgomery, which is now recycling 13 percent of its waste, wants to reach a recycling goal of 30 percent by 1997. A phase-in of curbside collection of glass, cans and certain plastic containers is set to begin in mid-1991.

Even though Kramer characterized Montgomery as in the forefront of recycling, some critics say the county isn't doing enough. They say a more stringent effort could prove to be a safer and cheaper alternative to construction of a $250 million incinerator in Dickerson.

The County Council is set this week to begin its final review of the proposed contracts for the Dickerson burner. The council approved plans for the incinerator in a 4 to 3 vote in 1987, but some council members recently have expressed doubts about the project.

Montgomery will spend about $100,000 on an advertising and education campaign to get people to participate in recycling. While the newspaper separation is mandatory under county law and violations are punishable by fines, county officials said the stress will be on voluntary compliance.

"It's hard," said Esther Bowring, Montgomery's recycling director, "it's telling people what to do in their house with their trash . . . and people are very emotional about their garbage."

But once people figure out the logistics of where to store the newspapers and how to tie or bag them, "it's just like brushing your teeth," Bowring said. "You don't think anything about it after a while."

Bowring said up to 70 percent of residents now required to recycle their newpapers do so.

The newspapers collected, estimated to reach 26,000 tons in the first year of the expanded operation, will be processed into new newsprint by Southeast Recycling Corp. of Silver Spring, which operates a paper mill in Georgia. D.C. officials have had a hard time finding markets for the material collected there.

The other major source of trash targeted by Montgomery officials is yard waste, the leaves and grass clippings that account for 30 percent of residential waste.

County officials in July will ask residents in the midcounty to bag leaves and grass clippings in tall, decomposable 30-gallon paper bags, which they will have to purchase, for separate pickup. In 1992, the county will expand this special collection to lower county areas. County officials said households will receive instructions on how they must recycle.