Almost one-fourth of the nation's 18-year-old men required to register for the draft this year have failed to do so, Selective Service Director Thomas K. Turnage said yesterday.

Turnage, a retired National Guard major general, said he is "guardedly optimistic" that the 300,000 violators will register before the year ends.

Barry Lynn, former leader of a coalition of national organizations fighting draft registration and currently president of an antidraft information group, Draft Action, asserted yesterday that the figures confirm resistance is deepening.

"People who are supposed to register are unconvinced that it's an important obligation of citizenship," Lynn said. They believe, he said, that President Reagan "is serious about getting rid of registration, so why bother to register."

Reagan said during his campaign that he was opposed to compulsory registration and the draft. But he has stuck with the registration requirement imposed by former president Carter.

The failure of thousands to register is increasing pressure on Reagan to make a definitive statement on the issue. Selective Service officials believe that such a statement may come next month after the president has reviewed a report from his Task Force on Military Manpower.

That group met Friday to discuss what to do about the registration requirement but reached no final conclusions. A middle-ground position advocated by some specialists would eliminate compulsory registration but keep the Selective Service machinery intact by urging young men to register voluntarily at their local post offices.

Turnage said he senses widespread support for required registration for possible military duty. He cited a Harris Survey of Sept. 24 that said 83 percent of those polled favored compulsory registration.

"We're getting unanimous support from the governors," Turnage added. "We know of no significant major organization that is against registration."

He termed the registration drive, which started in 1980, a success despite the hundreds of thousands who have violated the law, which requires young men to register within a period of 30 days before or after their 18th birthday.

The Selective Service said its latest figures show that 1,336,000 men born in 1963 were supposed to register as of Sept. 1 and that 1,029,000, or 77 percent, did so. Turnage confirmed that as the largest number of violators in one year since Selective Service began keeping detailed records.

The closest parallel to today's situation, Selective Service officials said, came in 1973-74 when the nation had registration but no draft calls. The total of violators then was about 225,000 a year, officials said.

Young men born in 1960, 1961, 1962 and 1963 have been required to register upon reaching their 18th birthday. The rate of compliance has been dropping--95 percent for men born in 1960; 93 percent for 1961; 88 percent for 1962, and 77 percent so far for 1963.

Including the 307,000 men born in 1963 who have failed to register, refusals among those born from 1960-62 have brought the total of violators to 800,000, officials said.

The names of only 183 young men have been referred to the Justice Department for possible prosecution. Those names, the Selective Service said, came from people who sent them in on their own, often after hearing a young man brag about not registering. No cases have gone to trial.

"A lot of other names sent in didn't check out," a Selective Service official said. "A man would brag to his peers that he wasn't going to register, but our records showed that he had."