The Shubert Organization, which books the National Theatre, has proposed a tentative list of shows for the coming season--including the Pulitzer Prize-winning drama "Crimes of the Heart"--but claims it cannot confirm them until it has received assurances that proposed renovations of the playhouse will be completed by the fall.

The National has been closed since May 2. At that time, Maurice B. Tobin, chairman of the New National Theatre Corp. (NNTC), announced the summer months would be given over to needed repairs and alterations of the aged building and said it would reopen by Sept. 15.

Renovations, however, are not scheduled to begin until "sometime in July," according to James Crozier, a spokesman for Square 254, the development corporation responsible for the work. The delay, he said, was occasioned by the abrupt closing of the National, which gave Square 254 no time to prepare for the job.

The Shubert Organization claims that NNTC has not yet informed it of any construction dates, and therefore it cannot proceed with future bookings. Among the shows it is considering for the coming season at the National are "Broadway Babies," a pre-Broadway musical revue with a cast of 40 young performers, aged 6 to 11, to be directed by Tom O'Horgan; Beth Henley's "Crimes of the Heart"; the American premiere of the Royal Shakespeare Company's production of C.Y. Taylor's drama, "Good"; and return engagements of "Amadeus," "Sophisticated Ladies" and "Joseph and the Amazing Technicolor Dreamcoat."

"It's impossible for us to determine when the theater will be open," said Bernard Jacobs, president of the Shubert Organization, yesterday. "There was no reason to close that theater when they did. It never should have been dark all this time."

After protracted negotiations with NNTC, Square 254 plans to enlarge the mezzanine rest rooms over the summer, convert the heating and air-conditioning system from oil to electricity, undertake preliminary construction on an expanded lobby and make electrical improvements necessary for future work.

"We're shooting to finish by that magic date, Sept. 15," Crozier said. "Given the amount of work, it will probably be midnight, Sept. 14."

The construction delays and booking difficulties are part of the continuing problems facing NNTC, which has found itself embroiled in controversy recently with both the Shuberts and Square 254 over the future of the theater. Although the National had a highly popular season with such shows as "Evita" and "Pirates of Penzance," NNTC's latest financial statement shows a deficit of $20,431.96.

Meanwhile, Theater Lines, the Fairfax, Va., firm that has provided theater programs for the National since 1980, has withdrawn from its five-year contract. According to publisher Marius D. Prince, "Everything is so much up in the air, we had to bow out." Prince said the program lost money until January of this year, when advertising finally reached profitable levels. But the four-month dark period this summer, he explained, has broken the continuity in the advertising. "To start up again in the fall would put us in a losing position all over again," he said. Prince estimates his losses in publishing the program at "about $65,000."