President Reagan marked the fifth anniversary of his plan for a Star Wars missile defense system on Wednesday by asserting that the high-tech program is an incentive to U.S.-Soviet arms control efforts. In a written statement issued the same day he announced a date for his fourth summit with Soviet leader Mikhail S. Gorbachev, Reagan lauded the missile shield proposal, known formally as the Strategic Defense Initiative, as ``vital to our future security.'' ``We must recognize that we live in an imperfect, often violent world, one in which ballistic missile technology is proliferating despite our efforts to prevent this,'' Reagan said. ``We would be doing a grave and dangerous disservice to future generations if we assumed that national leaders everywhere, for all time, will be both peaceful and rational.'' The president warned, as he has many times, that the Soviets ``not only are ahead of us in ballistic missiles, but also are deeply engaged in their own SDI-like program. If they are allowed to keep their near-monopoly in defenses, we will be left without an effective means to protect our cherished freedoms in the future.'' The president announced his proposal for the missile shield defense program on March 23, 1983. ``I put forward the vision of ... a future free from the threat of the most dangerous weapon mankind has invented: fast-flying ballistic missiles,'' Reagan recalled in his statement. Reagan, who has staunchly defended the plan despite Soviet efforts to curb it and congressional efforts to cut its funding, said it had ``provided a valuable incentive for the Soviets to return to the bargaining table and to negotiate seriously over strategic arms reductions.'' ``And as we move toward lower levels of offense, it will be all the more important to have an effective defense,'' Reagan argued. The president has repeatedly insisted, however, that he will not use SDI as a bargaining chip in negotiations with the Soviets. Reagan, following an Oval Office meeting with Soviet Foreign Minister Eduard Shevardnadze, announced he will go to Moscow from May 29 to June 2 for his fourth meeting with Gorbachev. The highlight of the summitt was intended to be the signing of a treaty to slash the superpowers' long-range strategic weapons, but Reagan has suggested that the agreement will not be ready due to time limitations. White House spokesman Marlin Fitzwater said the issue of SDI did not come up in Wednesday's meetings between U.S. and Soviet officials at the White House. In his statement, Reagan said the high-tech program now faces problems that ``are largely political.'' Congress has cut funds for the program every year, Reagan said, asserting this has put the program ``one to two years'' behind schedule. Capitol Hill slashed Reagan's 1988 request for the program from $5.6 billion to $3.9 billion. He is seeking $4.6 billion in 1989. In the year's first defense spending vote, a House subcommittee decided Wednesday to cut deeply into Reagan's budget request for Star Wars, approving $3.7 billion, which would be an increase of only 3 percent over the current Star Wars budget, according to congressional sources speaking on condition of anonymity. The request will later go to the full House Armed Services Committee, and later to the full House.