The cost of an expanded fleet of Trident missile-carrying submarines could run $7 billion to $10 billion more than suggested by the Navy, the General Accounting Office says.

In a report on the status of the increasingly costly and production-delayed Trident and its nuclear missiles, the GAO said that if a fleet of 29 vessels were built the cost could reach more than $50 billion - $10 billion more than rough figures supplied to Congress by Navy planners.

A smaller fleet of 21 vessels could cost more than $37 billion, compared with a navy figure of $30 billion, the GAO said.

The congressional auditing agency, describing its own estimates as "conservative," called on Defense Secretary Harold Brown to provide detailed cost information. It said Congress and the GAO have urged the Pentagon for several years to estimate both the ultimate size and cost of a Trident fleet.

The first Trident, already expected to be a year late when it goes into service in 1981, has attracted attention because its cost has soared from an original estimate of $793 million to $1.2 billion, nearly a 50 percent increase. Other escalations have pushed overall costs of the original 14-ship program more than $1 billion beyond original estimates. The Tridents are being built by General Dynamics, which is embroiled in a $544 million claims dispute with the Navy over other submarines.

The GAO said the submarine construction "continues to face serious schedule delays because of low productivity, a shortage of skilled workers and late receipt of materials."

Continuing arms control negotiations and other factors have limited the approved program to 14 Tridents, but the final number is expected to go well beyond as older missile submarines are retired.

Last year, the Navy provided the House Appropriations Committee with projections for costs of 21 and 29 Tridents, but said they were "rough order of magnitude estimates" and not "budget-quality."

The GAO said, "The Navy's estimates do not include all relevant costs." It also said unplanned costs for the first 52 missiles - enough for two submarines with spares - could add about $50 million to their price tag.

Meanwhile, Rep. Les Aspin (D-Wis.) said yesterday that the contractor building the Trident missile submarines now says all five are 19 months behind schedule.

Aspin, a member of the House Armed Services Committee, released newly revised estimates about the submarines.

The Navy said last November that the average delay on the Trident submarines would be six months. It also predicted that although the first Trident would be a year late in delivery, the lag time would be cut to two months by the time the fifth was finished.

Aspin said the contractor is more pessimistic.

"Not even Pollyanna would assume that a construction schedule would improve over time, but that's what the navy predicted." Aspin said, adding that "the undying optimism of the Navy's planners is astounding."

"Shipyard delays have gone from bad to horrendous," he said in a statement.