President Bush's plan to deploy a limited missile defense system by 2004 is unlikely to provoke the fierce Democratic opposition that President Reagan's plan encountered almost two decades ago, lawmakers say.

But some Democrats say the technology behind the plan is unproven and they doubt it will offer much protection in the next few years.

Sen. Carl Levin, D-Mich, chairman of the Senate Armed Services Committee, said Bush's plan "violates common sense by determining to deploy systems before they have been tested and shown to work.''

Bush on Tuesday ordered the Pentagon to have ready within two years a bare-bones system for defending American territory, troops and allies against attack by ballistic missiles.

Development of missile defense systems was severely limited under the 1972 Anti-Ballistic Missile Treaty, which expired in June, six months after President Bush announced that Washington would withdraw from the 30-year old agreement.

In Moscow, the Russian Foreign Ministry issued a two-page statement Wednesday expressing regret over Bush's decision to push ahead with a missile defense system. The statement expressed concern the focus on the missile system will divert resources from "today's real challenges and threats ... international terrorism.''

The system would be expected to expand for years, eventually providing defense against all ranges of ballistic missiles, at every stage of their flight and from any point on the globe.

The administration put no final price tag on the project, but will ask Congress to allocate $1.5 billion over the next two fiscal years on top of the roughly $8 billion a year the Pentagon already has budgeted for missile defense. The extra money would pay for additional short-, medium- and long-range missile interceptors.

Democrats are unlikely to feel as strongly about Bush's plan as they had about Reagan's. Bush's proposal is more modest in scope and cost. Technology has advanced since the 1980s. And the 1972 Anti-Ballistic Missile Treaty, which opponents often cited in opposing missile defense programs, is no longer an issue. Bush withdrew the United States from the treaty last summer.

Rep. John Spratt of South Carolina, a leading Democrat on the House Armed Services Committee, said he doesn't believe his party will offer much of a challenge to Bush. "This strikes us as a best first step to take,'' he said.

Defense Secretary Donald H. Rumsfeld cautioned against viewing the plan as foolproof. He described the planned initial capability as "better than nothing'' and said it would evolve in ways that incorporate technological advances, lessons learned from testing and help from allies.

Rep. Curt Weldon, R-Pa., a senior member of the Armed Services Committee, said the plan needs to be seen as a first step.

"It's giving us a capability that we've never had and do not have today. If a missile were launched today there would be nothing we could do to take it down — nothing,'' said Weldon.

But Democrats said that capability won't exist for years. Spratt said key elements of the missile defense system are behind schedule or haven't been successfully tested. "We shouldn't fool ourselves about the capacity of the system,'' he said.

The most ambitious version of missile defense ever proposed was Reagan's 1983 Strategic Defense Initiative, dubbed "Star Wars'' by critics. He envisioned an impenetrable shield against the Soviet Union's arsenal of thousands of missiles. That effort foundered until it was killed by the Clinton administration.

Bush's hopes of winning support in Congress are helped by the GOP control of both houses next year. Sen. John Warner, R-Va., a strong supporter of missile defense, will become Armed Services chairman, replacing Levin.

Bush said his project, which has been in development for years and the subject of intense international debate, is an essential step toward providing defenses against 21st century threats. They include the possibility of terrorist groups launching ballistic missiles armed with chemical, biological or nuclear warheads.

Since January 2001, the Pentagon has been successful in four of five attempts to intercept a long-range warhead in space with an interceptor launched from Kwajalein Atoll in the central Pacific. But last week, in the most recent test, the interceptor rocket failed to destroy a dummy warhead.

The Pentagon has succeeded in three consecutive tests of a ship-launched interceptor, the Standard Missile-3, against medium-range missiles.