The Defense Department is likely to scrap its controversial, F15-launched antisatellite (ASAT) system if Congress votes to continue a ban on tests of the weapon against a target in space, Pentagon and congressional sources said yesterday.

Dubbed "the flying tomato can" and designed to be fired into space from a high-flying F15 fighter, the Air Force ASAT missile has been plagued by technical problems during much of its eight-year history. The Pentagon already has cut the number of ASAT bases from two to one, and reduced the number of missiles it planned to buy by two-thirds.

Pentagon officials, who now describe the troubled system as only the "first phase" of a broader ASAT program, said they will focus more on promising antisatellite technologies that are being developed as part of President Reagan's Strategic Defense Initiative research.

The demise of the F15-launched ASAT and a return by the United States to a program that is purely research would come as the Soviet Union is seeking a ban on all antisatellite systems as part of Moscow's latest offer on space weapons in the Geneva arms talks.

Until now, the Reagan administration has pushed the F15-launched missile on grounds that the Soviets already have an operational ASAT and the United States does not. Washington also argued against negotiating a ban on all types of antisatellite systems because such an agreement could not be verified.

Last year, Congress adopted restrictions which prohibit the Air Force from testing the current ASAT against a target in space, unless the Soviets undertake such a test. Consequently, the next two tests of the system, now scheduled for August and September, will target the radiant energy from a star, which is permitted by the congressional ban.

The congressional restrictions are expected to be renewed for the fiscal year beginning Oct. 1, and that would undercut Air Force plans for three tests against orbiting targets now scheduled for fiscal 1987. "Without those tests," a Pentagon official said, "there can be no confidence in proceeding with the system."

Last September, the Air Force ASAT successfully destroyed an obsolete satellite, but that is not considered sufficient by the Pentagon to persuade Congress to finance full production of the weapon, a military source said.

The House Armed Services Committee has deleted all procurement money sought by the Pentagon for fiscal 1987 and slashed the requested research funds. The full House is expected to add the testing restrictions. The Senate Armed Services Committee has agreed to the funds and to allow testing, but Rep. Les Aspin (D-Wis.), chairman of the House panel, is expected to hold firm when the testing issue reaches a conference committee since he is under fire from fellow Democrats for failing to support their positions on other issues.

Because of the restrictions now in force, the Air Force already dropped plans for two ASAT tests this year against an instrumented orbiting target launched last November. The $20 million space vehicle, which has two targets, is still in orbit.

Only one of the tests now planned against a star was part of the original test program. The other was added to gather additional data on the missile's infrared sensors, according to testimony given Congress earlier this year.

"Without targets," one Air Force official said recently, "there is only so much data of value that can be obtained."

In an April 26 letter, the Pentagon's undersecretary for research and engineering, Donald A. Hicks, described the F15-launched weapon as "only the first phase of a broader antisatellite capability" being studied. He said the Pentagon had "restructured the antisatellite program in January 1986 into two phases in recognition of the evolutionary nature of the threat, previous congressional actions and potential complementary systems."

The president's SDI, the so-called "Star Wars" research program, includes study of several laser and "kinetic kill" systems that possibly could be used against Soviet satellites as well as ballistic missile warheads.

Hicks' letter was included as part of a General Accounting Office (GAO) investigation of the F15-launched system that was sent to Congress June 11. The GAO criticized the program's cost growth, testing program, schedule delays and limited capability.

After the January review, the Pentagon cut planned production of the antisatellite missile from 112 to 35. The restructured program would cost $3.9 billion, slightly less than the $4.1 billion projected little more than a year ago for three times as many missiles, according to Aspin and Rep. George E. Brown Jr. (D-Calif.), two leading congressional critics of the program.

Originally, the Pentagon planned to base F15 antisatellite squadrons at McCord Air Force Base in Washington, and Langley Air Force Base, Va., in order to be able to attack Soviet satellites from two different points. With only one base, however, the area of coverage would be limited.

The GAO also said the testing program, as proposed by the Air Force, is not challenging enough. The instrumented targets and outdated U.S. satellites that the Air Force will use if congressional restrictions are lifted have different characteristics than Soviet satellites, according to the GAO. The Air Force Operational Test and Evaluation Center (AFOTEC), according to the GAO, said the instrumented targets "may be of limited value in projecting the system's performance in an operational environment."

The GAO also said that AFOTEC believes a "minimum of 15 flight tests is necessary to establish the system's capability," whereas only 12 are planned. The system's Air Force program office, however, did not agree, the GAO said.